The dissemination of protein conformational changes, which has been implicated in the transmission of prion diseases, is potentially an important mechanism in the dissemination of physiological signals. The proposed investigation is a study of the bacteriophage Mu repressor, which regulates the link between transposition and physiological signals by acting as a conformationally sensitive sensor. The repressor shuts down the phage transposition functions for the establishment of lysogeny, but it can be inactivated under conditions of stationary phase or starvation conditions by a mechanism dependent upon its carboxy-terminal domain (CTD). Dominant-negative forms of the repressor with an altered carboxy terminus called Vir not only are rapidly degraded by the host CIpXP protease but induce conformational changes in the unmodified wild-type repressor to promote its recognition by the protease. Truncated repressor molecules marked with a degradation tag, molecules that can arise from the stalling of the ribosome on mRNA, are also potent inducers that promote degradation or inactivation of the repressor. The CTD of the repressor modulates DNA binding and proteolytic degradation by movement that regulates DNA binding affinity and exposure of the CIpX recognition motif present at the C terminus. The hypothesis is that the target repressor responds to putative signal molecules that induce transposition by propagating a conformational change in the unmodified repressor population to promote their synchronous inactivation. Such signal molecules are postulated to be aborted products of repressor translation. The biological function of the repressor as a conformationally sensitive sensor will be examined by pursuing three specific aims: 1) Characterize repressor mutations and interactions that influence CTD movement, CTD exposure, DNA binding, and recognition by CIpXP protease; 2) determine whether the Mu repressor acts as a conformationally sensitive sensor for altered repressor forms produced under starvation or stationary phase conditions; and 3) examine the structure of the repressor by NMR and X-ray crystallography. Conformationally sensitive sensors may be useful in diagnosis of diseases involving abnormal protein conformations and may play an important role in regulating critical processes such as transposition that can influence cellular genome structure. ? ?
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