A physical and functional interaction between yeast Pol4 and Dnl4-Lif1 links DNA synthesis and ligation in nonhomologous end joining.

Department of Molecular Medicine and Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245-3207, USA.

Genetic studies have implicated the Saccharomyces cerevisiae POL4 gene product in the repair of DNA double-strand breaks by nonhomologous end joining. Here we show that Pol4 preferentially catalyzes DNA synthesis on small gaps formed by the alignment of linear duplex DNA molecules with complementary ends, a DNA substrate specificity that is compatible with its predicted role in the repair of DNA double-strand breaks. Pol4 also interacts directly with the Dnl4 subunit of the Dnl4-Lif1 complex via its N-terminal BRCT domain. This interaction stimulates the DNA synthesis activity of Pol4 and, to a lesser extent, the DNA joining activity of Dnl4-Lif1. Notably, the joining of DNA substrates that require the combined action of Pol4 and Dnl4-Lif1 is much more efficient than the joining of similar DNA substrates that require only ligation. Thus, the physical and functional interactions between Pol4 and Dnl4-Lif1 provide a molecular mechanism for both the recruitment of Pol4 to in vivo DNA double-strand breaks and the coupling of the gap filling DNA synthesis and DNA joining reactions that complete the microhomology-mediated pathway of nonhomologous end joining.

PMID: 12235149 [PubMed - indexed for MEDLINE]