title: Yeast Nej1 is a key participant in the initial end binding and final ligation steps of nonhomologous end joining.
abstract: In Saccharomyces cerevisiae, the key components of the nonhomologous end joining (NHEJ) pathway that repairs DNA double-strand breaks (DSBs) are yeast Ku (yKu), Mre11-Rad50-Xrs2, Dnl4-Lif1, and Nej1. Here, we examined the role of Nej1 in NHEJ by a combination of molecular genetic and biochemical approaches. As expected, the recruitment of Nej1 to in vivo DSBs is dependent upon yKu. Surprisingly, Nej1 is required for the stable binding of yKu to in vivo DSBs, in addition to Dnl4-Lif1. Thus, Nej1 and Dnl4-Lif1 are independently recruited by yKu to in vivo DSBs, forming a stable ternary complex that channels DSBs into the NHEJ pathway. In accord with these results, purified Nej1 interacts with yKu and preferentially binds to DNA ends bound by yKu. Furthermore, the binding of a mixture of Nej1 and Dnl4-Lif1 to DNA ends bound by yKu is greater than the sum of the binding of the individual proteins, indicating that pairwise interactions among yKu, Nej1, and Dnl4-Lif1 contribute to complex assembly at DNA ends. Nej1 stimulates intermolecular ligation by Dnl4-Lif1, but, more interestingly, the addition of Nej1 results in more than one intermolecular ligation per Dnl4 molecule. Thus, Nej1 not only plays an important role in determining repair pathway choice by participating in the initial NHEJ complex formed at DSBs but also contributes to the reactivation of Dnl4-Lif1 after repair is complete, thereby increasing the capacity of the NHEJ repair pathway.
authors.affiliation: Radiation Oncology Research Laboratory, Department of Radiation Oncology, and The Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Alan E
authors.initials: AE
authors.lastname: Tomkinson
mesh_terms: D053903:DNA Breaks, Double-Stranded; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair / Q000502:physiology*; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C114091:LIF1 protein, S cerevisiae; D046912:Multiprotein Complexes; C441270:NEJ1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C520769:YKU70 protein, S cerevisiae; D011088:DNA Ligases; D000072481:DNA Ligase ATP