Rho-dependence of Schizosaccharomyces pombe Pck2

Background: In metazoans, the HR1 domain, a motif found in a number of prot eins including the protein kinase C-related PRKs, is responsible for an int eraction with Rho-GTPases. The structural similarity between the Schizosacc aromyces pombe Pck proteins and the mammalian Rho-dependent protein kinase C-related family, has led us to investigate the relationship between the fu nction of Rho and that of Pck1/2. Results: Rho1 is shown to interact with the conserved N-terminal HR1 domain of Pck1/2 in vitro and in vivo. Lethal overproduction of Rho1 is neutraliz ed by co-expression of the Pck2 HR1 domain, which by itself compromises gro wth when overproduced. The Pck2-Rho1 interaction has a profound effect on t he steady state expression of Pck2 and this is shown to parallel the immuno precipitated activity and phosphorylation of Pck2 at its activation loop si te. It is further shown that Pck2 becomes localized at the septum, where Rh o1 is also located. Conclusions: The results demonstrate that the Pck proteins are Rho1 effecto rs in fission yeast and that the HR1 domain is a universal motif for the Rh o-GTPase interaction. Furthermore, the evidence supports the contention tha t the yeast Pck1 and Pck2 proteins are primitive protein kinases, which in vertebrates have evolved into the two distinct PKC and PRK families.