A prion-like domain of Tpk2 catalytic subunit of protein kinase A modulates P-body formation in response to stress in budding yeast

Abstract

Low complexity regions are involved in the assembly and disassembly of P-bodies (PBs). Saccharomyces cerevisiae contains three genes encoding the protein kinase A (PKA) catalytic subunit: TPK1, TPK2 and TPK3. Tpk2 and Tpk3 isoforms localize to PBs upon glucose starvation showing different mechanisms and kinetics of accumulation. In contrast to the other two isoforms, Tpk2 harbors a glutamine-rich prion-like domain (PrLD) at the N-terminus. Here we show that the appearance of Tpk2 foci in response to glucose starvation, heat stress or stationary phase was dependent on its PrLD. Moreover, the PrLD of Tpk2 was necessary for efficient PB and stress granule aggregation during stress conditions and in quiescent cells. Deletion of PrLD does not affect the in vitro and in vivo kinase activity of Tpk2 or its interaction with the regulatory subunit Bcy1. We present evidence that the PrLD of Tpk2 serves as a scaffold domain for PB assembly in a manner that is independent of Pat1 phosphorylation by PKA. In addition, a mutant strain where Tpk2 lacks PrLD showed a decrease of turnover of mRNA during glucose starvation. This work therefore provides new insight into the mechanism of stress-induced cytoplasmic mRNP assembly, and the role of isoform specific domains in the regulation of PKA catalytic subunit specificity and dynamic localization to cytoplasmic RNPs granules.