ClpAP is an auxiliary protease for DnaA degradation in Caulobacter crescentus.

The Clp family of proteases is responsible for controlling both stress responses and normal growth. In Caulobacter crescentus, the ClpXP protease is essential and drives cell cycle progression through adaptor-mediated degradation. By contrast, the physiological role for the ClpAP protease is less well understood with only minor growth defects previously reported for ΔclpA cells.

Mec1 is one of multiple kinases that prime the Mcm2-7 helicase for phosphorylation by Cdc7.

Activation of the eukaryotic replicative DNA helicase, the Mcm2-7 complex, requires phosphorylation by Cdc7/Dbf4 (Dbf4-dependent kinase or DDK), which, in turn, depends on prior phosphorylation of Mcm2-7 by an unknown kinase (or kinases). We identified DDK phosphorylation sites on Mcm4 and Mcm6 and found that phosphorylation of either subunit suffices for cell proliferation. Importantly, prior phosphorylation of either S/T-P or S/T-Q motifs on these subunits is required for DDK phosphorylation of Mcm2-7 and for normal S phase passage.

Incorporation into the prereplicative complex activates the Mcm2-7 helicase for Cdc7-Dbf4 phosphorylation.

The essential S-phase kinase Cdc7-Dbf4 acts at eukaryotic origins of replication to trigger a cascade of protein associations that activate the Mcm2-7 replicative helicase. Also known as Dbf4-dependent kinase (DDK), this kinase preferentially targets chromatin-associated Mcm2-7 complexes that are assembled on the DNA during prereplicative complex (pre-RC) formation. Here we address the mechanisms that control the specificity of DDK action.