Interaction of nick-directed DNA mismatch repair and loop repair in human cells.
In human cells, large DNA loop heterologies are repaired through a nick-directed pathway independent of mismatch repair. However, a 3'-nick generated by bacteriophage fd gene II protein heterology is not capable of stimulating loop repair. To evaluate the possibility that a mismatch near a loop could induce both repair types in human cell extracts, we constructed and tested a set of DNA heteroduplexes, each of which contains a combination of mismatches and loops. We have demonstrated that a strand break generated by restriction endonucleases 3' to a large loop is capable of provoking and directing loop repair. The repair of 3'-heteroduplexes in human cell extracts is very similar to that of 5'-heteroduplex repair, being strand-specific and highly biased to the nicked strand. This observation suggests that the loop repair pathway possesses bidirectional repair capability similar to that of the bacterial loop repair system. We also found that a nick 5' to a coincident mismatch and loop can apparently stimulate the repair of both. In contrast, 3'-nick-directed repair of a G-G mismatch was reduced when in the vicinity of a loop (33 or 46 bp between two sites). Increasing the distance separating the G-G mismatch and loop by 325 bp restored the efficiency of repair to the level of a single base-base mismatch. This observation suggests interference between 3'-nick-directed large loop repair and conventional mismatch repair systems when a mispair is near a loop. We propose a model in which DNA repair systems avoid simultaneous repair at adjacent sites to avoid the creation of double-stranded DNA breaks.
Huang
Yao-Ming
YM
School of Medical Technology, National Taiwan University, Taipei, Republic of China.
Chen
Shee-Uan
SU
Goodman
Steven D
SD
Wu
Shang-Hsin
SH
Kao
Jau-Tsuen
JT
Lee
Chun-Nan
CN
Cheng
Wern-Cherng
WC
Tsai
Keh-Sung
KS
Fang
Woei-horng
WH
D020137:Base Pair Mismatch; D020029:Base Pairing; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004260:DNA Repair; D004720:Endonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes; D010957:Plasmids / Q000378:metabolism; D013379:Substrate Specificity; D013997:Time Factors
D009692:Nucleic Acid Heteroduplexes; D004247:DNA; D004720:Endonucleases