THE CHIMERIC VIRA-TAR RECEPTOR PROTEIN IS LOCKED INTO A HIGHLY RESPONSIVE STATE

The wild-type VirA protein is known to be responsive not only to pheno lic compounds but also to sugars via the ChvE protein (G. A. Cangelosi , R. G. Ankenbauer, and E. W. Nester, Proc. Natl. Acad. Sci. USA 87:67 08-6712, 1990, and N. Shimoda, A. Toyoda-Yamamoto, J. Nagamine, S. Usa mi, M. Katayama, Y. Sakagami, and Y. Machida, Proc. Natl. Acad. Sci. U SA 87:6684-6688, 1990). It is shown here that the mutant VirA(Ser-44, Arg-45) protein and the chimeric VirA-Tar protein are no longer respon sive to sugars and the ChvE protein. However, whereas the chimeric Vir A-Tar protein was found to be locked in a highly responsive state, the VirA(Ser-44, Arg-45) mutant protein appeared to be locked in a low re sponsive state. This difference turned out to be important for tumorig enicity of the host strains in virulence assays on Kalanchoe daigremon tiana.