Bi-directional processing of DNA loops by mismatch repair-dependent and -independent pathways in human cells

Scott D. McCulloch, Liya Gu, Guo Min Li

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Previous work has shown that small DNA loop heterologies are repaired not only through the mismatch repair (MMR) pathway but also via an MMR-independent pathway in human cells. However, how DNA loop repair is partitioned between these pathways and how the MMR-independent repair is processed are not clear. Using a novel construct that completely and specifically inhibits MMR in HeLa extracts, we demonstrate here that although MMR is capable of bi-directionally processing DNA loops of 2, 4, 5, 8, 10, or 12 nucleotides in length, the repair activity decreases with the increase of the loop size. Evidence is presented that the largest loop that the MMR system can process is 16 nucleotides. We also show that strand-specific MMR-independent loop repair occurs for all looped substrates tested and rigorously demonstrate that this repair is bi-directional. Analysis of repair intermediates generated by the MMR-independent pathway revealed that although the processing of looped substrates with a strand break 5′ to the heterology occurred similarly to MMR (i.e. excision is conducted by exonucleases from the pre-existing strand break to the heterology), the processing of the heterology in substrates with a 3′ strand break is consistent with the involvement of endonucleases.

Original languageEnglish (US)
Pages (from-to)3891-3896
Number of pages6
JournalJournal of Biological Chemistry
Issue number6
StatePublished - Feb 7 2003

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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