The NLS sequence of Prs3 is paramount for the maintenance of the cell wall integrity (CWI) pathway in Saccharomyces cerevisiae

Lithium, a natural Gsk3 inhibitor and a mood stabiliser for the treatment of bipolar disorder inhibits the growth of yeast when PRS1, PRS3 or PRS5 have been deleted indicating an involvement of Prs in neuropathology and cognitive deficits associated with central nervous system disorders, e.g., Charcot Marie Tooth disease (CMTX5). Prs5 is unusual in that it is one of the few triply phosphorylated proteins in yeast. Mutation of the three Prs5 phosphosites, S364, S367 and S369 and their neighbouring region negatively influences CWI as demonstrated by alterations in the phosphorylation pattern of the MAPK, Slt2 and in the expression of two targets, Rlm1 and Fks2, of the CWI pathway. Rim11, one of the four yeast Gsk3 paralogous proteins was verified as a partner of Prs5. The interaction of Prs5 with Rim11 was reduced following mutation of one or more of the three phosphosites. The argument for Rim11 being the kinase which phosphorylates Prs5 is strengthened since Prs5 contains a Gsk3-priming site C-terminal to the three phosphosites. Simultaneous deletion of PRS3 and PRS5 is synthetically lethal and is in fact, a triple deletant - prs1Δ prs3Δ prs5Δ, since deletion of the NLS, 284KKCPK288 of Prs3 results in the same phenotype as deletion of PRS3, i.e., concomitant loss of Prs1. Apart from Prs4, all other Prs proteins interact with the kinetochore-associated protein Nuf2 and the interaction of Prs3/Nuf2 is the strongest. Therefore, we postulate that three of the five Prs proteins, Prs1, Prs3 and Prs5, are required for correct CWI signalling by nucleocytoplasmic shuttling.