西亞試劑：Ku is a 5′-dRP/AP lyase that excises nucleotide damage near

Ku is a 5′-dRP/AP lyase that excises nucleotide damage near broken ends
Steven A. Roberts1, Natasha Strande1, Martin D. Burkhalter1, Christina Strom1, Jody M. Havener1, Paul Hasty2 & Dale A. Ramsden1

1 Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, and Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
2 Department of Molecular Medicine and Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, Texas 78245, USA

Top of pageMammalian cells require non-homologous end joining (NHEJ) for the efficient repair of chromosomal DNA double-strand breaks1. A key feature of biological sources of strand breaks is associated nucleotide damage, including base loss (abasic or apurinic/apyrimidinic (AP) sites)2. At single-strand breaks, 5′-terminal abasic sites are excised by the 5′-deoxyribose-5-phosphate (5′-dRP) lyase activity of DNA polymerase?β (pol?β)3, 4, 5, 6: here we show, in vitro and in cells, that accurate and efficient repair by NHEJ of double-strand breaks with such damage similarly requires 5′-dRP/AP lyase activity. Classically defined NHEJ is moreover uniquely effective at coupling this end-cleaning step to joining in cells, helping to distinguish this pathway from otherwise robust alternative NHEJ pathways. The NHEJ factor Ku can be identified as an effective 5′-dRP/AP lyase. In a similar manner to other lyases7, Ku nicks DNA 3′ of an abasic site by a mechanism involving a Schiff-base covalent intermediate with the abasic site. We show by using cell extracts that Ku is essential for the efficient removal of AP sites near double-strand breaks and, consistent with this result, that joining of such breaks is specifically decreased in cells complemented with a lyase-attenuated Ku mutant. Ku had previously been presumed only to recognize ends and recruit other factors that process ends; our data support an unexpected direct role for Ku in end-processing steps as well.

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