This is a possibility since ATP-competitive kinase inhibitors bind within a related ATP-binding pocket. Using a TSA screen, we identified 12 small molecules that significantly shifted the thermal stability of DDK. Several of these functioned comparatively to PHA-767491 in the assay: the Rho kinase inhibitor, the PKR inhibitor, and the Chk1 inhibitor. These compounds fall into different structural classes indicating that significant chemical space is available for new DDK inhibitor development. Interestingly, UCN-01, also a Chk1 inhibitor related to staurosporine, was also identified in our screen and showed a high affinity for DDK. This raises the possibility that more potent and selective derivatives of staurosporine might be designed against DDK. It also raises the possibility that reported biological effects due to Chk1 inhibition may be enhanced by the ability of SB218078 and/or UCN-01 to also inhibit DDK. Rockout is a pyridine-substituted indole derivative and so is somewhat related to PHA-767491. However, the position of the pyridine moiety on the indole ring of Rockout is quite different from the geometry of PHA-767491. The PKR inhibitor also falls into a distinct structural class from either PHA767491 or XL413. It was noteworthy that the PKR inhibitor blocked the growth of HCC1954 breast cancer cells, induced apoptosis, and inhibited DDK-mediated Mcm2 phosphorylation nearly as well as the lead DDK inhibitor PHA-767491. RNA-dependent protein kinase is ubiquitously expressed protein that blocks protein synthesis in response to a number of stresses and impacts both neurodegenerative diseases and cancer through its ability to promote apoptosis. The particular PKR inhibitor we used inhibited PKR with an IC50 of 210 nM but inhibited DDK with an IC50 of,70 nM in vitro, and so should be classified as a dual PKR/DDK inhibitor. Whether the PKR inhibitor induced apoptosis in HCC1954 cells due to inhibiting DDK activity, PKR activity or both remains to be determined. In summary, our results highlight the cross-reactivity of several kinase inhibitors with DDK and also reveal an opportunity to develop more potent, biologically active DDK inhibitors for future evaluation. Proteolysis of key regulatory factors is an important control element of gene activity both in eukaryotic and prokaryotic cells. In bacteria degradation by ATP-dependent proteases, belonging to the AAA+ superfamily, participates in regulation of many developmental pathways: the heat shock response, starvation adaptation, DNA damage repair, capsular polysaccharide biosynthesis, sporulation and control of bacteriophage development. Specific adaptor proteins are known to modify the interaction of substrates with ATP-dependent proteases. However, there are only three known intracellular inhibitory polypeptides. The phage T4 PinA protein ASP1517 inhibits the Lon protease, and both the Bacillus species sporulation regulator SpoVM and the phage l CIII inhibit the FtsH protease. Both FtsH inhibitors, SpoVM and CIII, were predicted to form amphipathic a helices and are degraded by FtsH. The FtsH protease is the only essential ATP-dependent protease in E. coli.. It is a membrane-bound homohexamer enzyme made of three major domains: a trans-membrane domain, an ATPase domain and a protease domain. FtsH is complexed with HflKC forming an FtsH6-HflKC6 holoenzyme, which is present in the cell in less than 100 copies. FtsH degrades membrane proteins and a number of LY2157299 cytoplasmic proteins such as LpxC, s32, SsrA-tagged proteins and the bacteriophage lCII and CIII proteins. Degradation of LpxC by FtsH is required for Escherichia coli viability, as the levels of LpxC are essential for maintaining the balance in the synthesis of phospholipids and lipopolysaccarides. Bacteriophage l infection may activate either the lytic or the lysogenic developmental pathway. In l infection, physiological conditions as low temperature, starvation of the cells and high multiplicity of infection are known to favor lysogeny. A few phage functions are specifically required for the lysogenic response.