Methylation of deoxycytidine incorporated by excision-repair synthesis of DNA.
Methylation of deoxycytidine incorporated by DNA excision-repair was studied in human diploid fibroblasts following damage with ultraviolet radiation, N-methyl-N-nitrosourea, or N-acetoxy-2-acetylaminofluorene. In confluent, nondividing cells, methylation in repair patches induced by all three agents is slow and incomplete. Whereas after DNA replication in logarithmic-phase cultures a steady state level of 3.4% 5-methylcytosine is reached in less than 2 hr after cells are labeled with 6- 3H-deoxycytidine, following ultraviolet-stimulated repair synthesis in confluent cells it takes about 3 days to reach a level of approximately 2.0% 5-methylcytosine in the repair patch. In cells from cultures in logarithmic-phase growth, 5-methylcytosine formation in ultraviolet-induced repair patches occurs faster and to a greater extent, reaching a level of approximately 2.7% in 10-20 hr. Preexisting hypomethylated repair patches in confluent cells are methylated further when the cells are stimulated to divide; however, the repair patch may still not be fully methylated before cell division occurs. Thus DNA damage and repair may lead to heritable loss of methylation at some sites.
D000099:Acetoxyacetylaminofluorene; D002455:Cell Division; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism; D005347:Fibroblasts; D006801:Humans; D008745:Methylation; D008770:Methylnitrosourea; D014466:Ultraviolet Rays
D003841:Deoxycytidine; D000099:Acetoxyacetylaminofluorene; D008770:Methylnitrosourea; D004247:DNA; C016569:5-methyldeoxycytidine