Note for: Nbs1 is essential for DNA repair by homologous recombination in higher vertebrate cells

(doi: 10.1038/nature01125)

It has been proposed that Rad50-Mre11-Nbs1 cpx possesses nuclease activity to create 3' single stranded tails.

Mre11-Rad50 are very conserved among yeast and human, except Xrs2 (homolog to Nbs1,Nijmegen breakage syndrome, in human also higher eukaryote).

NBS1 -- part of the NRM cpx and responsible for ATP-driven DNA unwinding and nuclease activity.

Mre1-null -- lethal in vertebrate cells, not yeast

Rad50 null -- lethal in vertebrate cells, not yeast

Nbs1 null is lethal in embryonic mice but not in DT40, therefore, we can study.

Mitomycin C relies on HR-mediated post-replicational repair.

NHEJ-end joining assay-

1. DT40 results in 29% microhomology

2. Ku70(-/-) - used 100% microhomology (lack of end-joining function)

SCneo-reporter construct;

1. transiently transfected I-Sce I enzyme

2. DSB is introduced by I-Sce I site in S2neo sequence-G418 resist-->HR mediated repair

First report on the involvement of Nbs1 in HR-repair.

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