Functional analysis of the replication fork proteome identifies BET proteins as PCNA regulators

Identifying proteins that function at replication forks is essential to understand DNA replication, chromatin assembly, and replication-coupled DNA repair mechanisms. Combining quantitative mass spectrometry in multiple cell types with stringent statistical cutoffs, we generated a high confidence catalogue of 593 proteins that are enriched at replication forks and nascent chromatin. Loss of function genetic analyses indicate that 85% yield phenotypes consistent with activities in DNA and chromatin replication or already have described functions in these processes. We illustrate the value of this resource by identifying activities of the BET family proteins BRD2, BRD3, and BRD4 in controlling DNA replication. These proteins use their extra-terminal domains to bind and inhibit the ATAD5 complex and thereby control the amount of PCNA on chromatin.