Equilibrium frequencies of α-globin genes

A mathematical model has been developed to study the mechanism of the maintenance of variable numbers of α-globin genes in human populations. The model incorporates both selection and unequal crossing-over. The selection is formulated so that a homozygous individual with a double deletion is lethal and a heterozygous individual with a deletion or addition of an α-globin gene in a chromosome has decreased fitness. This differs from the previous models of stabilizing selection studied by Ohta (1981) and Takahata (1981). The effect of random genetic drift on the α-thalassemia polymorphims has also been studied.It has been shown that, although the results obtained are compatible with the observation of the low frequency of triple α-globin loci, it cannot explain the high frequency of single and double deletions in Asian populations. For the latter case, some type of heterozygote advantage may be operating.     

MUC genes: a superfamily of genes? Towards a functional classification of human apomucins

The MUC genes encode epithelial mucins. Eight different human genes have been well characterized, and two others identified more recently. Among them, a family of four genes, expressed in the respiratory and digestive tracts, is clustered to chromosome 11p15.5; and these genes encode gel-forming mucins which are structurally related to the superfamily of cystine-knot growth factors. A second group is composed of three independent genes encoding various isoforms of mucins including membrane-bound mucins associated to carcinomas. In this second group, MUC3 and MUC4 encode large apomucins containing EGF-like domains.     

Identification of novel α-gliadin genes

Ten novel α-gliadin genes (Gli-ta, Gli-turg1, Gli-turg2, Gli-turg3, Gli-turg4, Gli-turg5, Gli-turg6, Gli-cs1, Gli-cs2, and Gli-cs3) with unique characteristics were isolated from wheat (Triticum aestivumL.), among which Gli-cs1, Gli-cs2, Gli-cs3, and Gli-turg6 were pseudogenes. Gli-cs3 and nine other sequences were much larger and smaller, respectively, than the typical α-gliadins. This variation was caused by insertion or deletion of the unique domain I and a polyglutamine region, possibly the result of illegitimate recombination. Consequently, Gli-cs3 contained 10 cysteine residues, whereas there were 2 cysteine residues only in the other nine sequences. Gli-ta/Gli-ta-like α-gliadin genes are normally expressed during the development of seeds. SDS-PAGE analysis showed that in-vitro-expressed Gli-ta could form intermolecular disulphide bonds and could be chain extenders. A protein band similar in size to Gli-ta has been observed in seed extracts, and mass spectrometry results confirm that the band contains small molecular mass α-gliadins, which is a characteristic of the novel α-gliadins. Mass spectrometry results also indicated that the two cysteine residues of Gli-ta/Gli-ta-like proteins participated in the formation of intermolecular disulphide bonds in vivo.     

The expression of three desaturase genes of Spirulina platensis in Escherichia coli DH5α – Heterologous expression of Spirulina-desaturase genes

The genes from a cyanobacterium--Spirulina platensis strain C1--that encode the acyl-lipid desaturases (desC, desA and desD) involved in gamma-linolenic (GLA) synthesis have been successfully expressed for the first time in Escherichia coli by employing a pTrcHisA expression system. In this report, the authors describe the expression of the three Spirulina N-terminal 6xHis-desaturases as well as the functional analysis of these recombinant proteins. The gene products of desC, desA and desD have approximate molecular masses of 37, 45, and 47 kDa, respectively. Enzymatic activity measurement of these products was carried out in vivo to demonstrate that (i) the expressed proteins are in functional form, and (ii) the cofactors of the host system can complement the system of Spirulina platensis. The study demonstrated that the gene products of desC and desA catalyzed the reactions in vivo where the enzyme substrates were provided in appropriate concentration. This indicates that the delta9 and delta12 desaturases were expressed in the heterologous host in their active form, and that these two reactions can be carried out in an E. coli host cell using its cofactors system. In contrast, delta6 desaturase activity can be detected only in vitro where electron carriers are provided. This suggests that while this enzyme is expressed in the heterologous host in its active form, its function in vivo is suppressed, as the electron carriers of the host system cannot complement the system of Spirulina platensis.     

Identification of dog T-cell receptor β chain genes

The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers D16409, D16410 and D16412     

Duplication of J κ genes within genus Rattus

We have isolated a region containing the immunoglobulin kappa chain joining segments from a liver DNA library of the Australian rat Rattus villosissimus, and determined its nucleotide sequence. While the laboratory rat (Rattus norvegicus) had previously been shown to contain three recently duplicated copies of J 2, R. villosissimus has only two. Furthermore, all three copies of J 2 in R. norvegicus share an 11 by deletion in their 5 flanking regions which is not evident in either copy of J 2 in R. villosissimus. This suggests that the initial duplication events occurred separately in the two lineages, and were followed by a second duplication in R. norvegicus, all three duplications having occurred within the last 6–12 million years (although more complicated schemes involving gene conversion events cannot be excluded). These results indicate that there is a high degree of plasticity in this region of the genome, and that selective forces must exist which have maintained the number of expressible J segments in humans (5) and rodents (4–6) within their narrow range.     

Is alternative splicing of mammalian genes conservative?

The conservation of alternative splicing in orthologous genes from the human and mouse genomes was analyzed. Alternatively spliced mouse genes from the AsMamDB database were used to scan the draft human genome. The mouse protein isoforms were aligned with respect to orthologous human genes, and thus the exon-intron structure of the latter was established. Proteins isoforms that could not be aligned throughout their length were analyzed in detail using the human EST alignment.     

Characterization of two β-glucosidase genes fromClostridium thermocellum

Summary Two -glucosidase genes, designatedbglA andbglB, were isolated from a gene bank ofClostridium thermocellum DSM 1237. The coding sequences forbglA andbglB were located on non-homologous DNA fragments of 3.2– and 3.4-kb, respectively. Both genes direct inEscherichia coli the synthesis of cytoplasmic -glucosidases, which differ with respect to substrate specificity and temperature profile. The properties of thebglA-encoded -glucosidase A closely resemble that of a -glucosidase previously isolated fromC. thermocellum cultures.     

Evolution of the rabbit immunoglobulin κ chain genes

We have analyzed the organization and the structure of rabbit chain genes encoding b allotypes in wild rabbits. The 1 gene of the b95 allotype was cloned and its structure determined. The J region is composed of five segments but only J2 appears to be functional and is identical to the J2 segment of the b4 allotype. The J region is highly conserved among the various b allotypes, whereas the constant region exon displays a high level of differences when compared with other allotypes (9%–30% of different amino acids). The b95 J region is closer to that of b4^var and the constant region to b5 allotype constant region. Alignment of nucleotide sequences revealed that the constant region exon displays segmental similarities with b4 and bas constant regions. The mosaic structure of b95 allotype gene indicates that complex allotypes of 1 genes may result from genetic exchanges of gene conversion between the different genes.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide database and have been assigned the accession number M22542. Address correspondence and offprint requests to: P.-A. Cazenave.     

Evolution of caprine and ovine β-defensin genes

Defensins comprise an important family of anti-microbial peptides. Among vertebrates, numerous defensin genes have been detected, but their evolutionary background is still discussed. We investigated the molecular evolution and variability of β-defensins of Caprini via sequence analyses of defensin introns. Screening of several domestic and wild species of Caprini revealed a total of 13 discrete β-defensin coding sequences, with three of them described before this study. Phylogenetic analyses revealed that the array of newly described defensin genes is of monophyletic origin and has arisen in numerous independent duplication events after separation of the ancestral defensins. As a result of that scenario, recent defensin genes are distributed in a species-specific manner. Values of synonymous and non-synonymous substitutions demonstrated that both modes of evolutionary pressure, positive as well as negative selection, have acted. In addition, conservation of some β-defensin exons is demonstrated. Discrimination of certain β-defensin genes was possible only due to intron-specific differences. Therefore, sequence analyses restricted to the exons would result in underestimation of the number of β-defensin genes. Our study shows that for reconstruction of the phylogenetic history data of defensin introns are more appropriated. Comparisons among the amino acid sequences show moderate substitutions without changing the net charge of the mature peptides. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Isolation and characterization of wheat ω-gliadin genes

The DNA sequences of two full-length wheat ω-gliadin prolamin genes (ωF20b and ωG3) containing significant 5′ and 3′ flanking DNA sequences are reported. The ωF20b DNA sequence contains an open reading frame encoding a 30,460-Dalton protein, whereas the ωG3 sequence would encode a putative 39,210-Dalton protein except for a stop codon at amino-acid residue position 165. These two ω-gliadin genes are closely related and are of the ARQ-/ARE-variant type as categorized by the derived N-terminal amino-acid sequences and amino-acid compositions. The ω-gliadins were believed be related to the ω-secalins of rye and the C-hordeins of barley, and analyses of these complete ω-gliadin sequences confirm this close relationship. Although the ω-type sequences from all three species are closely related, in this analysis the rye and barley ω-type sequences are the most similar in a pairwise comparison. A comparison of ω-gliadin flanking sequences with respect to that of their orthologs and with respect to wheat gliadin genes suggests the conservation of flanking DNA necessary for gene function. Sequence data for members of all major wheat prolamin families are now available. Received: 24 August 2000 / Accepted: 15 December 2000