Mutation analysis of the human radiosensitivity gene ATM and identification of related genes

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The ATM on chromosome 11q22.3 is the gene responsible for the human radiosensitive recessive disease ataxia-telangiectasia (A-T). Analysis of mutations of ATM and its related genes is a major subject of this study. (1) ATM mutations in Japanese A-T patients belonging to 8 different families were analyzed by two methods (REF : restriction endonuclease fingerprinting, PCR-SSCP). REF method detected 75% of mutations and the others were detected by PCR-SSCP.Mutations that lead to exon skipping or premature protein truncation were predominant. The two mutations 4612del165 and 7883del5 were found to be founder-effect mutations that may be predominant in Japanese ATM mutant alleles. (2) ATM mutations in human tumor cell lines were analyzed by PCR-SSCP to search for possible occurrence of somatic ATM mutations in non-AT patients. Analysis of 25 cell lines revealed 50 sequence alterations in 16 cell lines. None of them was identical to the mutations previously reported in A-T patients. The most … More striking feature was a high frequency of deletions within the intronic mononucleotide tracts in the 5 colon tumor cell lines with microsatellite instability. Some were associated with abnormal transcripts, implying that ATM is a novel mutation target of microsatellite instability where abnormal transcripts are generated indirectly by intronic mutations. (3) Mutations of 6 ATM-related genes (hRAD1, hRAD9, hRAD17, hHUS1, CHK1, CHES1 ) were analyzed in human tumor cell lines. Mutation frequency was very low compared with ATM.One missense polymorphism on hRAD17 was particularly intriguing because this site is highly conserved among species. (4) ATM-homologous sequences were analyzed to search for novel ATM-related genes. Southern blot analysis revealed a number of ATM-hybridizing bands outside chromosome 11. Among them, a 5.5-kb EcoRI fragment on chromosome 7 was analyzed. Sequence analysis of a 5442-bp fragment (p7LA5.5) cloned from chromosome 7-specific genomic library indicated 450-bp region around ATM exon 30 is included. This unprocessed pseudogene is supposed to be generated by a retrotransposition of a part of ATM gene. Further analysis of another ATM-hybridizing bands may lead to the identification of a novel functional gene that shares a motif with ATM. Less