Cyclobutane dimers and (6-4) photoproducts in human cells are mended with the same patch sizes.

J. E. Cleaver, J. Jen, W. C. Charles, D. L. Mitchell

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


The size of excision repair patches corresponding to excision of (6-4) pyrimidine-pyrimidone photoproducts and (5-5, 6-6) cyclobutane dimers have been independently determined by using bromodeoxyuridine substitution and density increases in isopycnic gradients of small DNA fragments. The two classes of photoproducts were distinguished by using (a) a xeroderma pigmentosum (XP) revertant cell line that excises (6-4) photoproducts normally, but does not excise cyclobutane dimers from bulk DNA or from an actively transcribed sequence; (b) an XP cell line containing the denV gene of bacteriophage T4, which repairs only cyclobutane dimers by a unique glycosylase mechanism, and (c) normal cells analyzed during time intervals in which cyclobutane dimer repair is the main repair process in action. The patch sizes for the two lesions were similar under all conditions and were estimated to be approximately 30-40 bases. These values are slightly large than corresponding estimates for Escherichia coli and Saccharomyces cerevisiae but close to estimates from in vitro experiments with human cell extracts. The size of 30 bases may consequently be very close to the actual distance between cleavage sites made on either side of a photoproduct during repair.

Original languageEnglish (US)
Pages (from-to)393-402
Number of pages10
JournalPhotochemistry and Photobiology
Issue number3
StatePublished - Sep 1991
Externally publishedYes

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • Biochemistry
  • Biophysics


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