The Cullin Rtt101p promotes replication fork progression through damaged DNA and natural pause sites

Accurate and complete DNA replication is fundamental to maintain genome integrity. While the mechanisms and underlying machinery required to duplicate bulk genomic DNA are beginning to emerge, little is known about how cells replicate through damaged areas and special chromosomal regions such as telomeres, centromeres, and highly transcribed loci [1]. Here, we have investigated the role of the yeast cullin Rtt101 Delta in this process. We show that rtt101 Delta cells accumulate spontaneous DNA damage and exhibit a G(2)/M delay, even though they are fully proficient to detect and repair chromosome breaks. Viability of rtt101 Delta mutants depends on Rrm3p, a DNA helicase involved in displacing proteinaceous complexes at programmed pause sites [2]. Moreover, rtt101 Delta cells show hyperrecombination at forks arrested at replication fork barriers (RFBs) of ribosomal DNA. Finally, rtt101 Delta mutants are sensitive to fork arrest induced by DNA alkylation, but not by nucleotide depletion. We therefore propose that the cullin Rtt101 Delta promotes fork progression through obstacles such as DNA lesions or tightly bound protein-DNA complexes via a new mechanism involving ubiquitin-conjugation.