Seminars

Chromosomes are copied only once per cell cycle. To ensure the faithful inheritance of genetic information, all stages of DNA replication must be tightly regulated. While much attention has been devoted to understanding how the replication machinery, termed the replisome, assembles and elongates, the mechanisms by which it is unloaded upon termination remain poorly understood. Using biochemical approaches, I have found that in human cells, the terminated replisome is ubiquitylated within its central motor - the CMG helicase by the cullin-RING E3 ubiquitin ligase CUL2LRR1. CUL2LRR1 specifically produces a K-48 linked ubiquitin chain on the MCM7 subunit of CMG via its substrate adaptor LRR1, marking the complex a substrate for disassembly by the p97/VCP segregase. This ubiquitylation reaction is dependent on cullin neddylation and proceeded through two steps: initial monoubiquitylation by the UBE2D class of E2 enzymes, followed by chain elongation mediated by the UBE2R or UBE2G E2 enzymes.