Molecular characterization of a novel form of (A gamma delta beta)zero-thalassemia deletion with a 3'' breakpoint close to those of HPFH-3 and HPFH-4: insights for a common regulatory mechanism.

We have molecularly characterized a novel (A gamma delta beta)zero-thalassemia associated with increased synthesis of HbF in three members of a German family. The levels of HbF in the peripheral blood red cells of the heterozygotes ranged between 9.9% and 12.5% with a heterocellular distribution in the red cells, as detected by immunofluorescence. The mutation resulted from a deletion starting about 1.5 to 1.9 kb from the 3' end of the G gamma-gene and ending 27 +/- 0.5 kb 3' to the beta-globin gene. Thus, the total deletion is 52 +/- 0.5 kb. Its 5' breakpoint is similar to that of the previously described (A gamma delta beta)zero-thalassemias, while the location of the 3' breakpoint is placed very close to the 3' breakpoints of HPFH-4 and HPFH-3 deletions. The proximity of the 3' breakpoint of the German (A gamma delta beta)zero-thalassemia to those of HPFH-3 and HPFH-4 deletions raises the possibility that a common mechanism, such as the juxtaposition of an enhancer, might underlie the activation of the gamma-globin genes in these three mutants.     

Recombination of bacteriophage phi X174 by the red function of bacteriophage lambda.

Recombination of bacteriophage phi X174 was effectively promoted when the Red function of lambda was supplied by either co-infection with lambda or induction of lambda lysogens. Mutations in red alpha and red beta genes of lambda abolished recombination nearly completely, whereas a mutation in gam gene reduced it only slightly. The Red-promoted recombination of phi X174 occurred in recA, recB, and polA mutants as well as in wild-type strains of Escherichia coli. It was further stimulated when phi X174 mutants were irradiated with UV light before infection.     

Inhibition of the recBCD-dependent activation of Chi recombinational hot spots in SOS-induced cells of Escherichia coli.

Nucleotide sequences called Chi (5'-GCTGGTGG-3') enhance homologous recombination near their location by the RecBCD enzyme in Escherichia coli (Chi activation). A partial inhibition of Chi activation measured in lambda red gam mutant crosses was observed after treatment of wild-type cells with DNA-damaging agents including UV, mitomycin, and nalidixic acid. Inhibition of Chi activation was not accompanied by an overall decrease of recombination. A lexA3 mutation which blocks induction of the SOS system prevented the inhibition of Chi activation, indicating that an SOS function could be responsible for the inhibition. Overproduction of the RecD subunit of the RecBCD enzyme from a multicopy plasmid carrying the recD gene prevented the induced inhibition of Chi activation, whereas overproduction of RecB or RecC subunits did not. It is proposed that in SOS-induced cells the RecBCD enzyme is modified into a Chi-independent recombination enzyme, with the RecD subunit being the regulatory switch key.     

Rec-Mediated Recombinational Hot Spot Activity in Bacteriophage Lambda II. a Mutation Which Causes Hot Spot Activity

Crosses have been performed which identify phage mutants (chi) which cause recombinational hot spot activity in lambda. The hot spot activity is found in crosses of red(-) gam(-) chi(-) strains in rec(+) hosts; in the crosses reported here, both the chi(-) mutations and the hot spot are located near the right end of the chromosome. The hot spot occurs in standard crosses as well as under conditions which block DNA synthesis, and is dependent on a functional host recB gene.-The chi mutation is shown to be dominant, but the tests do not show whether chi is a gene or a site.     

DNA Polymerase I-Dependent Mutants of Coliphage Lambda

Mutagenized lysates of bacteriophage lambda were screened for mutants unable to plate on DNA polymerase I-deficient (polA(-)) hosts. The mutants obtained were all recombination deficient (red(-)). These mutants, like red(-) and gam(-) mutants previously isolated by others, grow more poorly than wild-type lambda even on polA(+) hosts (burst size 14 to 30% of wild-type lambda.) In a polA(-) host, the burst size of red(-) and gam(-) mutants is reduced an additional five- to tenfold, and lysis is delayed. Wild-type lambda grows normally in polA(-) hosts. Neither lambdaN(-)nin (which doesn't express red or gam) nor lambdabio phages (from which all or part of the red-gam region is deleted) form plaques on polA(-) hosts. Apparent revertants, able to plate on polA(-) hosts, have been selected from both lambdaN(-)nin and lambdabio. Those derived from N(-)nin seem to be N(-)nin cro(-) mutants; whereas those coming from lambda bio have a new bypass mutation (pas) that lies between genes P and Q.     

Identification of a nonframeshift 84-bp deletion in exon 13 of the cystic fibrosis gene.

Cystic fibrosis (CF) is the most frequent autosomal recessive inherited disorder in Caucasian populations. The disease is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. We have identified an 84-bp deletion in exon 13 of the CFTR gene, detected by DNA amplification and direct sequencing of 500 bp of the 5' end of exon 13. The deletion was in the maternal allele of a CF patient bearing the delta F508 deletion in the father's allele. The same 84-bp deletion could also be detected in the patient's mother. The deletion spanned from a four-A cluster in positions 1949-1952 to another four-A cluster in positions 2032-2035, including 84 bp which correspond to codons 607-634 (1949del84). The reported mutation would result in the loss of 28 amino acid residues of the R domain of the CFTR protein.     

A low proportion of BRCA2 mutations in Finnish breast cancer families.

One hundred breast cancer families were identified at the Helsinki University Central Hospital in Finland and were screened for germ-line mutations in the coding regions and splice boundaries of the BRCA2 gene. Eight families (8%) were found to carry five different mutations, all of which are predicted to prematurely truncate the protein product. These BRCA2 families have early-onset breast cancer (mean and median age = 49 years), with four of the eight families including ovarian cancer but with no families including male breast cancer. A wide spectrum of other cancers also is seen in these families. Three mutations were identified in more than one family, and haplotype analysis in the families suggested a common founder for each recurrent mutation. One recurrent mutation, 999del5, previously has been noted as a common mutation in Iceland. The relationship between the Icelandic 999del5 mutation and the Finnish 999del5 mutation was explored by comparison of families from both countries. A common haplotype covering a minimal region intragenic to the BRCA2 gene was shared between the Icelandic and the Finnish mutation carriers.     

Functions antagonistic to plasmid formation by lambda N- chromosomes

It was concluded in the preceding paper that lambda N- cI- genomes probably failed to form plasmids within infected Escherichia coli cells because they leakily express functions that act to destabilize the plasmid state. This prediction was investigated by examining the effect upon plasmid-forming ability of the loss of possible anti-plasmid functions. The loss of Ter function was found to allow long-term plasmid formation, although the efficiency of initial plasmid formation and the heritable stability without selection were low. The combined loss of the int, red and gam gene functions also promoted plasmid growth, although the absence of Ter lambda was necessary. In contrast, the presence of Ter80 (due to an h80 substitution) did not prevent plasmid formation when the int, red and gam genes were absent, indicating that Ter80 does not attack the closed-circular form of the lambda chromosome. The combined loss of the ter, int, red and gam gene functions facilitated fully efficient inheritance of the lambda N- cI- plasmids in the absence of selection, although the efficiency of initial plasmid formation remained low. However, cells harbouring such plasmids suffered a decline in viability, indicating that the plasmids expressed a function (or more than one) that acts to debilitate the host cells--presumably an effect that is increased with this genotype because the modified lambda N- cI- plasmids are inherently more stable. The possible involvement of the lambda S and kil functions in destabilization is discussed.     

Genetic comparisons of patients with cystic fibrosis with or without meconium ileus. Clinical Centers of the French CF Registry.

Cystic fibrosis (CF) is an autosomal disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Neonatal meconium ileus (MI) occurs in 10-20 percent of newborns with CF. The purpose of this study was to determine the allelic frequencies of the CF mutation in French patients with and without MI and the incidence of MI in 7 homozygotes or compound heterozygotes for mutation of the CFTR gene. Our study confirms the positive association between delta F508, the most frequent CF mutation, G542X mutation and MI and a negative association with G551D.     

Identification of sbcD mutations as cosuppressors of recBC that allow propagation of DNA palindromes in Escherichia coli K-12.

The function of an open reading frame (orf-45) located upstream of the sbcC gene of Escherichia coli was investigated. Mutations that inactivate sbcC improve the ability to propagate lambda red gam phage that carry a palindromic sequence in their DNA. They also act with sbcB mutations as cosuppressors of the defects in recombination, DNA repair, and cell viability associated with recBC mutations. A 1,282-bp cassette encoding resistance to kanamycin was used to disrupt orf-45. The mutation, which has a polar effect on the expression of sbcC, allowed stable propagation of palindromic lambda phage even when the sbcC gene product was provided in trans. Additional nonpolar mutations in orf-45 were isolated on the basis of their ability to improve the growth of recBC sbcB strains. These mutations also confer resistance to mitomycin C, allow efficient recombination in Hfr crosses, and facilitate stable propagation of palindromic phage. It is concluded that the products of orf-45 and sbcC are functionally related. The orf-45 gene is therefore renamed sbcD.     

Partial uncoupling of the mitochondrial membrane by a heterozygous null mutation in the gene encoding the gamma- or delta-subunit of the yeast mitochondrial ATPase

Prior genetic studies indicated that the yeast mitochondrial ATP synthase can be assembled into enzyme complexes devoid of the gamma-, delta-, or epsilon-subunits (Lai-Zhang, J., Xiao, Y., and Mueller, D. M. (1999) EMBO J. 18, 58-64). These subunit-deficient complexes were postulated to uncouple the mitochondrial membrane thereby causing negative cellular phenotypes. This study provides biochemical and additional genetic data that support this hypothesis. The genetic data indicate that in a diploid cell, a heterozygous deletion mutation in the gene encoding the gamma- or delta-subunit of the ATPase is semidominant negative due to a decrease in the gene number from 2 to 1. However, the heterozygous atp2Delta mutation is epistatic to the heterozygous mutation in the gene encoding gamma or delta, suggesting that the semidominant negative effect is because of a gain of activity in the cells. Biochemical studies using mitochondria isolated from the yeast strains that are heterozygous for a mutation in gamma or delta indicate that the mitochondria are partially uncoupled. These results support the hypothesis that the negative phenotypes are caused by the formation of a gamma- or delta-less ATP synthase complex that is uncoupled.     

Thermo-inducible expression of cloned early genes of bacteriophage Mu.

An EcoRI fragment, containing approx. 5100 base pairs (bp) of the immunity-end of bacteriophage Mu, was inserted into the multicopy plasmid pMB9 by in vitro recombination. The expression of early Mu genes, located on the cloned fragment, is thermo-inducible because of the presence of the ts mutation in gene c. The isolation of a transformant harbouring the recombinant plasmid, pGP1, was possible only when expression of Mu genes was prevented. pGP1 can be maintained at 28 degrees C at high copy number, but at 42 degrees C the pGP1 containing cells are killed due to the expression of the kil gene of Mu. The following Mu genes are present on pGP1: the ner gene, the integration and replication genes A and B, the cim gene, and the kil gene. pGP1 containing cells do not show Gam and Sot activity at 42 degrees C, therefore the leftmost EcoRI site on the Mu DNA is located between genes kil and gam or sot, or within the gam or sot gene.     

Genetic background modifies inner ear and eye phenotypes of jag1 heterozygous mice

Mice heterozygous for missense mutations of the Notch ligand Jagged1 (Jag1) exhibit head-shaking behavior indicative of an inner ear vestibular defect. In contrast, mice heterozygous for a targeted deletion of the Jag1 gene (Jag1del1) do not demonstrate obvious head-shaking behavior. To determine whether the differences in inner ear phenotypes were due to the types of Jag1 mutations or to differences in genetic background, we crossed Jag1del1 heterozygous mice onto the same genetic background as the missense mutants. This analysis revealed that variation of the Jag1 mutant inner ear phenotype is caused by genetic background differences and is not due to the type of Jag1 mutation. Genome scans of N2 backcross mice identified a significant modifier locus on chromosome 7, as well as a suggestive locus on chromosome 14. We also analyzed modifiers of an eye defect in Jag1del1 heterozygous mice from this same cross.     

Cloning of fragments of lambda phage DNA, containing red and gam genes

On the base of plasmid pCV20 (Apr, Tcr mol. weight 5.2 x 10(6) a recombinant plasmid pEH60 (Apr, mol. weight 17.0 x 10(6) with BamHI fragment of phage DNA, containing red+ and gam+ genes was constructed. Selection was found on the ability of phage red- and gam- to propagate in strain E. coli K12 recA-, which was transformed by recombinant plasmid with active red and gam genes. Influence of recombinant plasmid pEH60 on processes of repair and recombination of phage lambda DNA and bacterial DNA was studied. It was shown that red gene in plasmid pEH60 compensates deficiency of redA gene in these processes with phage lambda DNA; in the case of E. coli K12 AB2480 uvr- recA- (pEH60) the processes of multiple reactivation and decombination of phage red- were presented. In the case of bacterial cells, plasmid pEH60 did not compensate deficiency of recA function of bacteria, although it partly compensates deficiency of recBC function. Increase of survival after introduction of plasmid pEH60 in the cell was obtained only for recBC- strain, but not for wild type and recA- strains.     

RAD10, an excision repair gene of Saccharomyces cerevisiae, is involved in the RAD1 pathway of mitotic recombination.

The RAD10 gene of Saccharomyces cerevisiae is required for the incision step of excision repair of UV-damaged DNA. We show that the RAD10 gene is also required for mitotic recombination. The rad10 delta mutation lowered the rate of intrachromosomal recombination of a his3 duplication in which one his3 allele has a deletion at the 3' end and the other his3 allele has a deletion at the 5' end (his3 delta 3' his3 delta 5'). The rate of formation of HIS3+ recombinants in the rad10 delta mutant was not affected by the rad1 delta mutation but decreased synergistically in the presence of the rad10 delta mutation in combination with the rad52 delta mutation. These observations indicate that the RAD1 and RAD10 genes function together in a mitotic recombination pathway that is distinct from the RAD52 recombination pathway. The rad10 delta mutation also lowered the efficiency of integration of linear DNA molecules and circular plasmids into homologous genomic sequences. We suggest that the RAD1 and RAD10 gene products act in recombination after the formation of the recombinogenic substrate. The rad1 delta and rad10 delta mutations did not affect meiotic intrachromosomal recombination of the his3 delta 3' his3 delta 5' duplication or mitotic and meiotic recombination of ade2 heteroalleles located on homologous chromosomes.     

Regional distribution of heterozygous 657del5 mutation carriers of theNBS1 gene in Wielkopolska province (Poland)

The homozygous 657del5 mutation, called Slavic mutation, of the NBS1 gene, causes the Nijmegen Breakage Syndrome (NBS). This syndrome is connected with a high incidence of malignancies in early childhood. A high frequency of NBS heterozygotes was found among patients with melanoma, breast, ovary and prostate cancer. The aim of our research was to determine the frequency of 657del5 mutation of the NBS1 gene in the population of Wielkopolska province. For this purpose, we analysed blood samples from anonymous Guthrie cards. In a group of 2090 newborns from the whole province, we found 16 heterozygous mutation carriers. The frequency of 1/131 is higher than 1/190 reported for populations from other regions in Poland. We observed differential regional distribution of heterozygous 657del5 mutation carriers within the province: among 464 samples from the eastern part of Wielkopolska we found 6 carriers (1/77), in contrast to the southern part without any carrier among 625 samples analysed. The high mean frequency of heterozygous 657del5 mutation (1/131) in Wielkopolska province may be associated with cancer incidence in this region.     

Effects of recB21, recF143, and uvrD152 on recombination in lambda bacteriophage-prophage and Hfr by F- crosses.

The effects of the mutation pairs recB21 recF143 and recB21 uvrD152 on the frequency of genetic recombination were investigated in lambda phage-prophage crosses under homoimmune conditions. To prevent recombinants from being formed by the phage red system, these experiments were performed with phages and prophages carrying red and gam mutations. Both spontaneous and damage-induced recombination was measured, the phages being either undamaged or treated with trimethylpsoralen and 360-nm light to cross-link the phage DNA. Control and damaged phages were allowed to infect lysogenic host cells under conditions in which phage gene expression was repressed and phage DNA replication was blocked by lambda immunity. Although the double mutations recB21 recF143 and recB21 uvrD152 reduced recombination in Hfr by F- crosses to 0.3 to 0.02% of the wild-type controls, the presence of these pairs of mutations in the host lysogens had relatively little effect on the results of the phage-prophage crosses. In the latter system, recB21 recF143 reduced spontaneous and damaged-induced recombination by less than threefold whereas recB21 uvrD152 increased it to three times the wild-type level, the increase being attributable to the uvrD mutation. Evidently, the gene products of recB,C uvrD, and recF wee not needed for lambda phage-prophage recombination under repressed conditions.     

A common and recurrent 13-bp deletion in the autoimmune regulator gene in British kindreds with autoimmune polyendocrinopathy type 1.

Autoimmune polyendocrinopathy type 1 (APS1) is an autosomal recessive disorder characterized by autoimmune hypoparathyroidism, autoimmune adrenocortical failure, and mucocutaneous candidiasis. Recently, an autoimmune regulator gene (AIRE-1), which is located on chromosome 21q22.3, has been identified, and mutations in European kindreds with APS1 have been described. We used SSCP analysis and direct DNA sequencing to screen the entire 1,635-bp coding region of AIRE-1 in 12 British families with APS1. A 13-bp deletion (964del13) was found to account for 17 of the 24 possible mutant AIRE-1 alleles, in our kindreds. This mutation was found to occur de novo in one affected subject. A common haplotype spanning the AIRE-1 locus was found in chromosomes that carried the 964del13 mutation, suggesting a founder effect in our population. One of 576 normal subjects was also a heterozygous carrier of the 964del13 mutation. Six other point mutations were found in AIRE-1, including two 1-bp deletions, three missense mutations (R15L, L28P, and Y90C), and a nonsense mutation (R257*). The high frequency of the 964del13 allele and the clustering of the other AIRE-1 mutations may allow rapid molecular screening for APS1 in British kindreds. Furthermore, the prevalence of the 964del13 AIRE-1 mutation may have implications in the pathogenesis of the more common autoimmune endocrinopathies in our population.     

Study of a single BRCA2 mutation with high carrier frequency in a small population.

Germ-line changes in the cancer-predisposition gene BRCA2 are found in a small proportion of breast cancers. Mutations in the BRCA2 gene have been studied mainly in families with high risk of breast cancer in females, and male breast cancer also has been associated with BRCA2 mutations. The importance of germ-line BRCA2 mutations in individuals without a family history of breast cancer is unknown. The same BRCA2 mutation has been found in 16/21 Icelandic breast cancer families, indicating a founder effect. We determined the frequency of this mutation, 999del5, in 1,182 Icelanders, comprising 520 randomly selected individuals from the population and a series of 632 female breast cancer patients (61.4% of patients diagnosed during the study period) and all male breast cancer patients diagnosed during the past 40 years. We detected the 999del5 germ-line mutation in 0.6% of the population, in 7.7% of female breast cancer patients, and in 40% of males with breast cancer. The mutation was strongly associated with onset of female breast cancer at age <50 years, but its penetrance and expression are varied. A number of cancers other than breast cancer were found to be increased in relatives of mutation carriers, including those with prostate and pancreatic cancer. Furthermore, germ-line BRCA2 mutation can be present without a strong family history of breast cancer. Comparison of the age at onset for mother/daughter pairs with the 999del5 mutation and breast cancer indicates that age at onset is decreasing in the younger generation. Increase in breast cancer incidence and lower age at onset suggest a possible contributing environmental factor.     

Distribution of the CCR5 gene 32-basepair deletion in 11 Chinese populations

A mutant allele of the chemokine receptor gene CCR5 bearing a 32-basepair deletion (delta 32CCR5) could increase the resistance to HIV-1 infection or delayed progression to AIDS. The frequency of this mutation is higher in Europeans than in Asians. To investigate the distribution of this polymorphism in China, 715 individuals from 11 Chinese populations were screened by PCR, including the Han and 10 other ethnic groups. The delta 32CCR5 gene was found in 16 individuals from 5 ethnic groups. All of them were heterozygous. The frequency of the mutant alleles of delta 32CCR5 is low in China and reflects (or might reflect) ancestral gene flow from Europe to Chinese ethnic groups and recent intermarriage within the ethnic groups.