Single and coincident intragenic mutations attributable to gene conversion in a human cell line.
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.
Giver
C R
CR
Environmental Toxicology Graduate Program, University of California, Riverside 92521, USA.
Grosovsky
A J
AJ
D002460:Cell Line; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics; D005091:Exons; D005785:Gene Conversion; D005819:Genetic Markers; D006579:Heterozygote; D006801:Humans; D008957:Models, Genetic; D009154:Mutation; D011110:Polymorphism, Genetic; D013937:Thymidine Kinase / Q000235:genetics
D005819:Genetic Markers; D013937:Thymidine Kinase; C092717:thymidine kinase 1