Open AccessSingle and Coincident Intragenic Mutations Attributable to Gene Conversion in a Human Cell Line
Author(s) -
Cynthia R. Giver,
Andrew J. Grosovsky
Publication year - 1997
Publication title -
genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.792
H-Index - 246
eISSN - 1943-2631
pISSN - 0016-6731
DOI - 10.1093/genetics/146.4.1429
Subject(s) - frameshift mutation , biology , genetics , heteroduplex , gene conversion , locus (genetics) , point mutation , allele , gene , exon , mutant , microbiology and biotechnology
Two polymorphic sites are located within the heterozygous TK1 locus in the human lymphoblastoid cell line TK6: an inactivating frameshift in exon 4 of the nonfunctional allele and a phenotypically silent frameshift in exon 7 of the functional allele. Through the use of these intragenic polymorphisms and microsatellite markers that flank TK1, we demonstrate that partial gene conversion accounts for 3/75 (0.04) spontaneous and 9/163 (0.06) X-ray-induced TK1- mutants, thus comprising a significant component of forward mutations at this locus. In all cases, the conversion tract is < 1 cM, rendering double exchange a remote alternate explanation for these results. Sequence analysis of full length TK1 cDNA provides rigorous exclusion of deletion events as a mechanism for generation of these allelotypes. Detailed examination of allelotypes in TK1- mutants identified two mechanisms for the generation of coincident sequence alterations that sometimes accompanied gene conversions. Mutations within the conversion tract were attributed to either error-prone gap filling synthesis during recombinational repair or mismatch repair within a heteroduplex region following branch migration. These findings suggest that a proportion of point mutations may not be targeted to sites of DNA base damage, but rather may arise as secondary consequences from the repair of DNA strand breaks.