sciP array data

Progression through the Caulobacter cell cycle is driven by the master regulator CtrA, an essential two-component signaling protein that regulates the expression of nearly 100 genes. CtrA is abundant throughout the cell cycle except immediately prior to DNA replication. However, the expression of CtrA-activated genes is generally restricted to S-phase. We identify the conserved protein SciP (small CtrA inhibitory protein) and show that it accumulates during G1 where it inhibits CtrA from activating target genes. The depletion of SciP from G1 cells leads to the inappropriate induction of CtrA-activated genes and, consequently, a disruption of the cell cycle. Conversely, the ectopic synthesis of SciP is sufficient to inhibit CtrA-dependent transcription, also disrupting the cell cycle. SciP binds directly to CtrA without affecting stability or phosphorylation; instead SciP likely prevents CtrA from recruiting RNA polymerase. CtrA is thus tightly regulated by a protein-protein interaction which is critical to cell cycle progression. For the sciP depletion studies, the sciP depletion strain was grown to mid-exponential phase in rich media supplemented with xylose, synchronized, and swarmer cells released into either glucose or xylose. Following one cell cycle, swarmers were again isolated from the two conditions and compared directly on arrays. This was done in duplicate. For the sciP overexpression studies, a wild type strain harboring the plasmid pJS14-Pxyl-sciP was grown to mid-exponential phase and xylose added for 2 hours. A strain harboring an empty vector was treated identically. The two populations were compared directly on arrays. This was done in duplicate.