Creation and removal of embedded ribonucleotides in chromosomal DNA during mammalian Okazaki fragment processing.
J Biol Chem 1997;
272:22591-9. [PMID:
9278414 DOI:
10.1074/jbc.272.36.22591]
[Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Mammalian RNase HI has been shown to specifically cleave the initiator RNA of Okazaki fragments at the RNA-DNA junction, leaving a single ribonucleotide attached to the 5'-end of the downstream DNA segment. This monoribonucleotide can then be removed by the mammalian 5'- to 3'-exo-/endonuclease, a RAD2 homolog-1 (RTH-1) class nuclease, also known as flap endonuclease-1 (FEN-1). Although FEN-1/RTH-1 nuclease often requires an upstream primer for efficient activity, the presence of an upstream primer is usually inhibitory or neutral for removal of this 5'-monoribonucleotide. Using model Okazaki fragment substrates, we found that DNA ligase I can seal a 5'-monoribonucleotide into DNA. When both ligase and FEN-1/RTH-1 were present simultaneously, some of the 5'-monoribonucleotides were ligated into DNA, while others were released. Thus, a 5'-monoribonucleotide, particularly one that is made resistant to FEN-1/RTH-1-directed cleavage by extension of an inhibitory upstream primer, can be ligated into the chromosome, despite the presence of FEN-1/RTH-1 nuclease. DNA ligase I was able to seal different monoribonucleotides into the DNA for all substrates tested, with an efficiency of 1-13% that of ligating DNA. These embedded monoribonucleotides can be removed by the combined action of RNase HI, cutting on the 5'-side, and FEN-1/RTH-1 nuclease, cleaving on the 3'-side. After FEN-1/RTH-1 action and extension by polymerization, DNA ligase I can join the entirely DNA strands to complete repair.
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