Complementation and characterization of the nested Rz and Rz1 reading frames in the genome of bacteriophage λ

Transposon insertions in the Rz gene of bacteriophage λ block lysis if the medium contains divalent cations at concentrations greater than 5?mM, but otherwise cause no change in phenotype. The Rz protein is thought to have an endopeptidase activity, previously reported in λ lysates, which might be involved in cleavage of oligopeptide crosslinks between glycosidic strands in the peptidoglycan and the Lpp lipoproteins of the outer bacterial membrane. Recently, a small lipoprotein has been reported as the product of a short reading frame, designated Rz1, in the +1 register within Rz. This protein has been detected in membranes of induced λ lysogens. To determine whether Rz1 has a function in the λ vegetative cycle, amber nonsense alleles of Rz and Rz1 have been constructed by site-directed mutagenesis and used for complementation and suppression analysis. Both Rzam and Rz1am alleles have phenotypes identical to those of the original Rz insertion alleles, and complement and are fully suppressed in a supE host, indicating that the two genes are independent, trans-acting genes encoding proteins required for lysis in the presence of cations. Moreover, supF suppresses Rzam but not the Rz1am mutation, and the defective Rz1am product in the supF host shows a partially dominant character and significantly retards lysis even in the absence of additional cations in the medium. Rz and Rz1 represent a unique example of two genes located in different reading frames in the same nucleotide sequence, which encode different proteins that are both required in the same physiological pathway.     

Rz/Rz1 lysis gene equivalents in phages of Gram-negative hosts

Under usual laboratory conditions, lysis by bacteriophage lambda requires only the holin and endolysin genes, but not the Rz and Rz1 genes, of the lysis cassette. Defects in Rz or Rz1 block lysis only in the presence of high concentrations of divalent cations. The lambda Rz and Rz1 lysis genes are remarkable in that Rz1, encoding an outer membrane lipoprotein, is completely embedded in the +1 register within Rz, which itself encodes an integral inner membrane protein. While Rz and Rz1 equivalents have been identified in T7 and P2, most phages, including such well-studied classic phages as T4, P1, T1, Mu and SP6, lack annotated Rz/Rz1 equivalents. Here we report that a search strategy based primarily on gene arrangement and membrane localization signals rather than sequence similarity has revealed that Rz/Rz1 equivalents are nearly ubiquitous among phages of Gram-negative hosts, with 120 of 137 phages possessing genes that fit the search criteria. In the case of T4, a deletion of a non-overlapping gene pair pseT.2 and pseT.3 identified as Rz/Rz1 equivalents resulted in the same divalent cation-dependent lysis phenotype. Remarkably, in T1 and six other phages, Rz/Rz1 pairs were not found but a single gene encoding an outer membrane lipoprotein with a C-terminal transmembrane domain capable of integration into the inner membrane was identified. These proteins were named "spanins," since their protein products are predicted to span the periplasm providing a physical connection between the inner and outer membranes. The T1 spanin gene was shown to complement the lambda Rz-Rz1- lysis defect, indicating that spanins function as Rz/Rz1 equivalents. The widespread presence of Rz/Rz1 or their spanin equivalents in phages of Gram-negative hosts suggests a strong selective advantage and that their role in the ecology of these phages is greater than that inferred from the mild laboratory phenotype.     

Identification and functional analysis of the Rz/Rz1-like accessory lysis genes in the membrane-containing bacteriophage PRD1

Bacteriophage PRD1 is a tailless membrane-containing double-stranded (ds) DNA virus infecting a variety of Gram-negative bacteria. In order to affect cell lysis, like most dsDNA phages, PRD1 uses the holin-endolysin system. In this study, we identified two accessory lysis genes, XXXVI and XXXVII , coding for proteins P36 and P37, respectively. Using genetic complementation assays, we show that protein pair P36/P37 is a functional and interchangeable analogue of the Rz/Rz1 of bacteriophage λ. Utilizing molecular biology, electrochemical as well as various microscopic techniques, we characterized the lysis phenotypes of PRD1 host cells infected with mutant viruses. Our results indicate that proteins P36 and P37 confer a competitive advantage to the phage by securing the efficient disruption of the infected cell and consequent release of the phage progeny under less favourable growth conditions. In concordance with prior data and the results obtained in this study, we propose a model explaining the role of Rz/Rz1-like proteins in the lysis process: Rz/Rz1 complexes transform the mechanical stress caused by the holin lesion at the CM to the OM leading to its disintegration. Finally, identification of the Rz / Rz1 -like genes in PRD1 suggests that tailless icosahedral phages are involved in genetic trade with tailed bacteriophages.     

The Rz1 gene product of bacteriophage lambda is a lipoprotein localized in the outer membrane of Escherichia coli

The Rz1 gene of bacteriophage λ is located within the Rz lysis gene. It codes for the 6.5-kDa prolipoprotein (Rz1) which undergoes N-terminal signal sequence cleavage and post-translational lipid modification of the N-terminal Cys of the mature protein. Globomycin, the antibiotic which inhibits bacterial signal peptidase II, specific for prolipoproteins containing diacylglyceryl cysteine [Hayashi and Wu, J. Bioenerg. Biomembr. 22 (1990) 451–471] inhibits the N-terminal sequence cleavage of the Rz1 precursor. The mature protein is rich in Pro, which constitutes 25% of its amino acids (aa). Using a computer-predicted, synthetic, 15-aa antigenic determinant of Rz1 polyclonal anti-Rz[46–60] antibodies, were obtained, and employed to localize Rz1 in bacterial fractions. In induced Escherichia coli λ lysogens Rz1 was found almost exclusively in the outer membrane (OM). In a strain overproducing Rz1 from the pSB54 plasmid, it was distributed in all the fractions. OM, fraction A and inner membrane (IM). Expression of Rz1 from the pSB54 caused enlargement of fraction A, corresponding to the adhesion sites of OM and IM. Such an enlargement was previously observed in induced λ lysogens, shortly before the onset of lysis.     

Inheritance of resistance to beet necrotic yellow vein virus in Beta vulgaris conferred by a second gene for resistance

Rhizomania is a serious disease of sugar beet, caused by beet necrotic yellow vein virus (BNYVV). The disease can only be controlled by the use of resistant cultivars. The accession Holly contains a single dominant gene for resistance, called Rz. The identification of a locus for resistance that differs from Rz would provide possibilities to produce cultivars with multiple resistance to BNYVV. Inheritance of resistance to BNYVV was studied by screening progenies of crosses between resistant plants of the accessions Beta vulgaris subsp. maritima WB42 and B. vulgaris subsp. vulgaris Holly-1–4 or R104. Observed and expected segregation ratios were compared to elucidate whether the resistance genes in the three accessions are alleles or situated on different loci. STS markers, linked to the genes for resistance, were used to study the segregation in more detail. The results demonstrated that the genes for resistance to BNYVV inHolly-1-4 and WB42 are closely linked. The gene for resistance in R104 is at the same locus as in Holly-1-4, and also closely linked to the gene in WB42. As the Holly resistance gene has been named Rz, the name Rz2 is proposed to refer to the resistance gene in WB42. Consequently, the gene Rz should be referred to as Rz1. Received: 29 October 1998 / Accepted: 12 March 1999     

The final step in the phage infection cycle: the Rz and Rz1 lysis proteins link the inner and outer membranes

Bacteriophage lambda has four adjacent genes -S, R, Rz and Rz1- dedicated to host cell lysis. While S, encoding the holin and antiholin, and R, encoding the endolysin, have been intensively studied, the products of Rz and Rz1 have not been characterized at either the structural or functional levels. Rz1 is an outer membrane lipoprotein and our results indicate that Rz is a type II signal anchor protein. Here we present evidence that an Rz-Rz1 complex that spans the periplasm carries out the final step in the process of host lysis. These results are discussed in terms of a model where endolysin-mediated degradation of the cell wall is a prerequisite for conformational changes in the Rz-Rz1 complex leading to the juxtaposition and fusion of the IM and OM. Fusion of the two membranes removes the last physical barrier to efficient release of progeny virions.     

P2 growth restriction on an rpoC mutant is suppressed by alleles of the Rz1 homolog lysC

Escherichia coli strain 397c carries a temperature-sensitive mutation, rpoC397, that removes the last 50 amino acids of the RNA polymerase beta' subunit and is nonpermissive for plating of bacteriophage P2. P2 gor mutants productively infect 397c and define a new gene, lysC, encoded by a reading frame that extensively overlaps the P2 lysis accessory gene, lysB. The unusual location of lysC with respect to lysB is reminiscent of the Rz/Rz1 lysis gene pair of phage lambda. Indeed, coexpression of lysB and lysC complemented the growth defect of lambda Rz/Rz1 null mutants, indicating that the LysB/C pair is similar to Rz/Rz1 in both gene arrangement and function. Cells carrying the rpoC397 mutation exhibited an early onset of P2-induced lysis, which was suppressed by the gor mutation in lysC. We propose that changes in host gene expression resulting from the rpoC397 mutation result in changes in the composition of the bacterial cell wall, making the cell more susceptible to P2-mediated lysis and preventing accumulation of progeny phage sufficient for plaque formation.     

Identification of a holin encoded by the<Emphasis Type="Italic">Streptomyces aureofaciens</Emphasis> phage µ1/6; functional analysis in<Emphasis Type="Italic">Escherichia coli</Emphasis> system

An open reading frame encoding an 88 amino acid protein was present downstream of the previously characterized endolysin ofStreptomyces aureofaciens phage μ1/6. Structural analysis of its sequence revealed features characteristic for holin. This open reading frame encoding the putative holin was amplified by polymerase chain reaction and cloned into the expression vector pET-21d(+). Synthesis of the holin-like protein resulted in bacterial cell death but not lysis. Theholμ1/6 gene was able to complement the defective λS allele in the nonsuppressingEscherichia coli HB101 strain to produce phage progeny. This fact suggests that the proteins encoded by both phage genes have analogous function,i.e. the streptomycete holin induces nonspecific lesions in the cytoplasmic membrane, through which the λ endolysin gains an access to its substrate, the cell wall. The concomitant expression of bothS. aureofaciens holμ1/6 and λ endolysin inE. coli resulted in abrupt cell lysis. This result provided further evidence that the product ofholμ1/6 gene is a holin. This work was supported by the VEGA grant of theSlovak Academy of Sciences no. 2/5070/25 and grant of theMinistry of Agriculture of the Slovak Republic no. 2003 5P27/0208 E02.     

SNP/haplotype associations in cytokine and cytokine receptor genes and immunity to rubella vaccine

An effective immune response to vaccination is, in part, a complex interaction of alleles of multiple genes regulating cytokine networks. We conducted a genotyping study of Th1/Th2/inflammatory cytokines/cytokine receptors in healthy children (n = 738, 11–19 years) to determine associations between individual single-nucleotide polymorphisms (SNPs)/haplotypes and immune outcomes after two doses of rubella vaccine. SNPs (n = 501) were selected using the ldSelect-approach and genotyped using Illumina GoldenGate™ and TaqMan assays. Rubella-IgG levels were measured by immunoassay and secreted cytokines by ELISA. Linear regression and post hoc haplotype analyses were used to determine associations between single SNPs/haplotypes and immune outcomes. Increased carriage of minor alleles for the promoter SNPs (rs2844482 and rs2857708) of the TNFA gene were associated with dose-related increases in rubella antibodies. IL-6 secretion was co-directionally associated (p ≤ 0.01) with five intronic SNPs in the TNFRSF1B gene in an allele dose-related manner, while five promoter/intronic SNPs in the IL12B gene were associated with variations in IL-6 secretion. TNFA haplotype AAACGGGGC (t-statistic = 3.32) and IL12B promoter haplotype TAG (t-statistic = 2.66) were associated with higher levels of (p ≤ 0.01) rubella-IgG and IL-6 secretion, respectively. We identified individual SNPs/haplotypes in TNFA/TNFRSF1B and IL12B genes that appear to modulate immunity to rubella vaccination. Identification of such “genetic fingerprints” may predict the outcome of vaccine response and inform new vaccine strategies.     

The Lysis System of the <Emphasis Type="Italic">Streptomyces aureofaciens</Emphasis> Phage μ1/6

Previously, two genes, designated as lyt and hol, were identified in the lysis module of phage μ1/6. They were cloned and expressed in Escherichia coli. An additional candidate holin gene, hol2, was found downstream from the hol gene based on one predicted transmembrane domain and a highly charged C-terminal sequence of the encoded protein. Expression of hol or hol2 in E. coli was shown to cause cell death. The concomitant expression of λ endolysin (R) and μ1/6 holin resulted in cell lysis. Similarly, the coexpression of the endolysin and holin of phage μ1/6 led to lysis, apparently due to the ability of μ1/6 endolysin to hydrolyze the peptidoglycan layer of this bacterium. In contrast, the simultaneous expression of μ1/6 hol2 and the endolysin gene (λR or μ1/6 lyt) did not cause detectable lysis of the host cells. Demonstration of the holin function in streptomycetes was achieved by providing for the release of μ1/6 endolysin to the periplasm and subsequent cleavage of the peptidoglycan, which strongly suggested that the holin produces lesions in the streptomycete membrane.     

MHC class II DRB1 gene polymorphism in the pathogenesis of Maedi–Visna and pulmonary adenocarcinoma viral diseases in sheep

Ovine pulmonary adenocarcinoma (OPA) and Maedi–Visna (Maedi) are two chronic respiratory diseases of retroviral origin which occur worldwide. It is known that different host genetic factors influence the outcome of viral infections. To determine if variation in the Mhc-DRB1 gene was associated with progression to these ovine diseases, sheep lungs with and without OPA and Maedi lesions were collected. A sequence-based method was applied and 40 different alleles were detected in the sample analysed. In the allele-by-allele association analysis, allele DRB1*0325 had a significant association with susceptibility to Maedi (P = 0.045). For OPA, DRB1*0143 and DRB1*0323 were significantly associated with susceptibility (P = 0.024 and P = 0.029), and allele DRB1*0702 was significantly associated with resistance (P = 0.012). Based on these results, the Mhc-DRB1 alleles were classified by effect in three categories—susceptible (S), resistant (R) and neutral (N)—and animals were reassigned the genotypes as S/S, S/R, S/N, R/R, R/N and N/N. In a second analysis, penalised logistic regression models including a flock effect were run. In Maedi, significant association was detected for the N/S heterozygote (P = 0.0007), but not for the S/S homozygote, probably as a result of the low number of S/S animals. In OPA, association was detected for both the S/S and R/R homozygotes (P = 0.005 and P = 0.047). This allele grouping method may be applied in association studies with highly variable genes. This is the first study demonstrating significant associations between sheep Mhc-DRB1 alleles and susceptibility to OPA and Maedi. Therefore, both diseases are suitable candidates for more comprehensive genetic studies.     

Inheritance of high palmitic acid content in the seed oil of sunflower mutant CAS-5

 Sunflower genotypes with increased levels of palmitic acid (C16 : 0) in the seed oil could be useful for food and industrial applications. The objective of the present study was to determine the inheritance of the high C16 : 0 content in the sunflower mutant line CAS-5 (>25% of the total oil fatty acids). This mutant was reciprocally crossed with the lines HA-89 (5.7% C16 : 0) and BSD-2-691 (5.4% C16 : 0), the latter being the parental line from which CAS-5 was isolated. No maternal effect for the C16 : 0 content was observed from the analysis of F₁ seeds in any of the crosses. The inheritance study of the C16 : 0 content in F₁, F₂ and BC₁F₁ seeds from the crosses of CAS-5 with its parental line BSD-2-691 indicated that the segregation fitted a model of two alleles at one locus with partial dominance for the low content. The analysis of the fatty acid composition in the F₂ populations from the crosses with HA-89 revealed a segregation fitting a ratio 19 : 38 : 7 for low (<7.5%), middle (7.5–15%), and high (>25%) C16 : 0 content, respectively. This segregation was explained on the basis of three loci (P1, P2, P3) each having two alleles showing partial dominance for low content. The genotypes with a high C16 : 0 content were homozygous for the recessive allele p1 and for at least one of the other two recessive alleles, p2 or p3. This model was further confirmed with the analysis of the F₃ and the BC₁F₁ generations. It was concluded that both the recessive alleles p2 and p3 were already present in the BSD-2-691 line, the allele p1 being the result of a mutation from P1. This genetic study will facilitate breeding strategies associated with the incorporation of the high C16 : 0 trait into agronomically acceptable sunflower hybrids. Received: 30 March 1998 / Accepted: 13 August 1998     

A novel role for the mating type (MAT) locus in the maintenance of cell wall integrity in Saccharomyces cerevisiae.

The cell wall and stress response component (Wsc) protein family in the yeast Saccharomyces cerevisiae is encoded by at least three genes, WSC1, WSC2, and WSC3. The Wsc proteins are putative upstream activators of the RHO1-regulated PKC1-MAP kinase cascade, and are required for maintenance of cell wall integrity and the stress response. Deletion of WSC1 causes a cell lysis defect that is exacerbated by deleting WSC2 or WSC3. This cell lysis defect can be rescued by adding osmotic stabilizers, such as 1 M sorbitol, to the medium, and by overexpressing PKC1 or RHO1. To advance our understanding of the function of the WSC genes, we performed a genetic screen to identify other components of the pathways they regulate. Here we report our findings. MAT a 1 and MATα2 were identified as dosage-dependent suppressors of the lysis defect of a wscΔ mutant. Overexpression of MAT a 1 or MATα2 was found to suppress the heat shock sensitivity, in addition to the lysis defect, of the wscΔ mutant. Phenotypic suppression by these two genes, MAT a 1 and MATα2, is significantly stronger when they are overexpressed in cells of the opposite mating type. Deletion of MAT a 1 exacerbates the lysis defect of haploid and diploid wscΔ strains. Our results suggest that the MAT locus plays a role in responses similar to those regulated by WSC and provide evidence for a regulatory effect of the MAT locus outside the realm of cell type determination. Received: 24 September 1998 / Accepted: 22 February 1999     

Microsatellites in Cassava (Manihot esculenta Crantz): discovery, inheritance and variability

 Fourteen microsatellites containing GA-repeats were isolated and characterized in cassava (Manihot esculenta Crantz, Euphorbiaceae). Microsatellite heterozygosity (h) was estimated in 48 accessions using (³²P)-end-labeled primers and in more than 500 accessions using fluorescence-based genotyping. Heterozygosity values ranged from 0.00 to 0.88 and the number of alleles detected varied from 1 to 15. The reproducibility of allele sizing was also assessed using fluorescence-based genotyping. The average inter-gel size difference was 1.03 nucleotides. Chi-square tests (χ²) were performed to analyse segregation distortion and the linkage between alleles segregating from either or both parents in an F₁ mapping population. Most microsatellite loci segregated in the expected 1 : 1, 1 : 2 : 1 or 1 : 1 : 1 : 1 ratio. Linkage was detected between loci segregating from either parent, and segregation distortion from the male parent was detected for locus GA-131. Approximately 80% of the microsatellites detected one or two alleles per accession, suggesting a low degree of microsatellite locus duplication, an unexpected finding for a putative allopolyploid, highly heterozygous species. The high h values of most microsatellites, their amplification in other Manihot taxa and their suitability for high-throughput, fluorescence-based genotyping, make microsatellites the marker of choice for germplasm characterization and saturation of the cassava map. Received: 4 September 1997 / Accepted 16 March 1998     

Ovine progressive pneumonia provirus levels associate with breed and Ovar-DRB1

Previous studies initiated defining the role of host genetics in influencing the outcome of exposure to ovine progressive pneumonia virus. However, specific genes influencing host control of virus replication and disease progression have not been identified. This study, using 383 ewes of the Columbia, Polypay, and Rambouillet breeds, tested the hypothesis that host control of OPPV as measured by provirus levels in the peripheral blood associates with certain breeds and MHC class II Ovis aries (Ovar)-DRB1 expressed alleles. Rambouillet ewes were less likely to have measurable provirus levels as compared to Columbia ewes at ages 5 and 6 (P value < 0.02), and they exhibited lower provirus levels when compared to both Columbia and Polypay ewes of the same ages (P value < 0.05). The presence of DRB1*0403- or DRB1*07012-expressed alleles were significantly associated (P value = 0.019 and 0.0002, respectively) with lower OPP provirus levels but only were only found in 11% of the ewe flock. Analysis of each segregating amino acid in the β1 domain of DR β-chain revealed that amino acids Y31, T32, N37, T51, Q60, or N74 significantly associated (P value range = 0.0003–0.018) with lower OPP provirus levels, whereas amino acids H32, A38, or I67 associated (P value range = 0.013–0.043) with higher OPP provirus levels. These results suggest that Ovar-DRB1 contributes as one host genetic factor that controls OPP provirus levels, but does not fully account for the breed-specific OPP proviral differences.     

Molecular dynamics simulations of Nafion and sulfonated polyether sulfone membranes. I. Effect of hydration on aqueous phase structure

We measured the water uptakes and proton conductivities of a Nafion membrane and three sulfonated polyether sulfone membranes (SPESs) with different values of ion-exchange capacity (IEC = 0.75, 1.0 and 1.4 meq/g) in relation to relative humidity in order to apply the findings to polymer electrolyte membrane fuel cells. The number of water molecules per sulfonic acid group λ at each humidity level was independent of the relative humidity for all membranes, but the proton conductivities of the SPESs were inferior to that of Nafion for the same λ value. Classical molecular dynamics simulations for the same membranes were carried out using a consistent force field at λ = 3, 6, 9, 12 and 15. The structural properties of water molecules and hydronium ions at a molecular level were estimated from radial distribution functions and cluster size distributions of water. We found that the radial distribution function of S(sulfonic acid)–S(sulfonic acid) of Nafion at λ = 3 indicated a significant correlation between the S–S pair, due to water channels, while the S–S pair of the SPESs showed a poor correlation. The cluster size distribution of water was also calculated in order to estimate the connectivity of the water channel. It is clear that some water is present in the SPESs as small, isolated clusters, especially when the water content is low.     

Molecular dynamics simulations of nafion and sulfonated poly ether sulfone membranes II. Dynamic properties of water and hydronium

We measured the self-diffusion coefficients of water in a Nafion membrane and two sulfonated polyethersulfone (SPES) membranes with varying ion-exchange capacities (IEC) in terms of relative humidity using the pulse field gradient NMR (PFG-NMR) technique. The self-diffusion coefficients were plotted against the number of water molecules per sulfonic acid group, λ, and compare these values with the results of molecular dynamics (MD) simulations. Classical MD simulations for all membranes were carried out using a consistent force field at λ = 3, 6, 9, 12, and 15. The dynamic properties of water (H₂O) and hydronium (H₃O⁺) on a molecular level were estimated as self-diffusion coefficients and residence times around a sulfonate group ( \textSO₃^- {\text{SO}}_3^{-} ). The diffusion coefficients of H₂O and H₃O⁺ followed the order, Nafion > SPES with IEC = 1.4 > SPES with IEC = 1.0 > SPES with IEC = 0.75, which agreed with the experimental data. The residence time distribution of H₂O around \textSO₃^- {\text{SO}}_3^{-} in Nafion was in the range of 1–6 ps, whereas H₂O in the SPES exhibited a residence time of greater than 20 ps.     

The lambda spanin components Rz and Rz1 undergo tertiary and quaternary rearrangements upon complex formation

Phage holins and endolysins have long been known to play key roles in lysis of the host cell, disrupting the cytoplasmic membrane and peptidoglycan (PG) layer, respectively. For phages of Gram‐negative hosts, a third class of proteins, the spanins, are involved in disrupting the outer membrane (OM). Rz and Rz1, the components of the lambda spanin, are, respectively, a class II inner membrane protein and an OM lipoprotein, are thought to span the entire periplasm by virtue of C‐terminal interactions of their soluble domains. Here, the periplasmic domains of Rz and Rz1 have been purified and shown to form dimeric and monomeric species, respectively, in solution. Circular dichroism analysis indicates that Rz has significant alpha‐helical character, but much less than predicted, whereas Rz1, which is 25% proline, is unstructured. Mixture of the two proteins leads to complex formation and an increase in secondary structure, especially alpha‐helical content. Moreover, transmission electron‐microscopy reveals that Rz–Rz1 complexes form large rod‐shaped structures which, although heterogeneous, exhibit periodicities that may reflect coiled‐coil bundling as well as a long dimension that matches the width of the periplasm. A model is proposed suggesting that the formation of such bundles depends on the removal of the PG and underlies the Rz–Rz1 dependent disruption of the OM.     

Polymorphism in intron 1 of the interferon-gamma gene influences both serum immunoglobulin E levels and the risk for chronic hepatitis B virus infection in Polynesians

Intron 1 of the interferon-gamma (IFNG) gene contains two polymorphisms. The 12 CA-repeat allele of the +875 IFNGCA microsatellite and the T allele of the +A874T single nucleotide polymorphism (SNP) have been associated with increased in vitro IFNG production and a variety of clinical phenotypes. The purpose of this study was to determine whether these polymorphisms influence total serum IgE levels [tsIgE] and the outcome of a hepatitis B virus (HBV) infection. IFNGCA and +A874T were typed in 186 asthmatics of Niuean ancestry and in Polynesian women with a chronic HBV infection (n = 60) and with natural immunity to the HBV (n = 66). The IFNGCA genotype was associated with [tsIgE] in asthmatic children (n = 51, p = 0.004) but not adults (n = 135, p = 0.87). The data were consistent with a co-dominant influence of the 12 CA-repeat allele on high [tsIgE]. The IFNGCA genotype was also associated with the risk for chronic HBV infection (χ ² = 11.6, p = 0.003) because of a dominant effect of the 12 CA-repeat allele on developing natural immunity in homozygotes (OR = 5.8, p = 0.003) and heterozygotes (OR = 2.7, p = 0.01). Similar associations were found for the T allele of the +A874T SNP. The possibility that these associations were due to linked alleles in the adjacent 783 bp of the promoter and 3′-untranslated region of the IFNG gene was excluded by direct sequencing. In summary, high-IFNG-producing alleles in intron 1 of the IFNG locus are associated with high [tsIgE] in asthmatic children from Niue and with natural immunity to the HBV in Polynesian women. These findings are consistent with a previous report of an association between +875 IFNGCA and [tsIgE] and provide preliminary evidence of a new association with the outcome of an HBV infection.     

Additive and testcross genetic variances in crosses among recombinant inbreds

 Breeders desire populations with a high mean performance and a large genetic variance. Theory and methods are lacking for predicting additive variance (V _A ) and testcross variance (V _T ) in biparental populations. Breeders have unsuccessfully attempted to predict V _A based on the coefficient of coancestry ( f ) or molecular-marker similarity between parents. In this paper, we derive the expected values of V _A and V _T in biparental populations, examine the variability of V _A among biparental crosses, and discuss how V _A and V _T may be predicted in applied breeding programs. Suppose i is a recombinant inbred derived from the cross between inbreds P ₁ and P ₂, and inbred j is not a direct descendant of i. Let V _A(i,j) be the additive variance in the F₂ of the (i×j) biparental cross. Let V _T(i, j) be the variance among testcrosses of F₂ individuals with a specific unrelated inbred or population. Assuming linkage equilibrium and the absence of epistasis, V _A(i, j) =λV _A(P1, j) +(1−λ) V _A(P2, j) , where λ= parental contribution of P ₁ to i. Similarly, V _T(i, j) = λV _T(P1, j) +(1−λ) V _T(P2, j) . Additive variance in crosses between recombinant inbreds cannot be modelled as a function of  f if, as indicated in the literature, V _A differs among crosses of founder inbreds. If molecular-marker similarity between parents is used as an estimate of f, then a strong linear relationship is likewise not expected between V _A and marker similarity. Differences between the actual and expected λ led to variation in V _A . In applied breeding programs, modelling V _A or V _T in biparental crosses may be feasible with estimates of V _A or V _T in prior crosses and information on λ obtained from molecular-marker data. Received: 23 September 1997 / Accepted: 30 December 1997