Protein complex Ppz1p/Hal3p and the efficiency of nonsense suppression in yeasts Saccharomyces cerevisiae

It is known that the efficiency of nonsense suppression in yeasts is controlled both genetically and epigenetically. Since many components of translation machinery are represented by phosphoproteins, the efficiency depends, in particular, on the activity of kinases and phosphatases that include the Ppz1p/Hal3p complex. It contains Ppz1p phosphatase, which is a catalytic subunit, and Hal3p that negatively regulates its function. The aim of this work was to study the mechanisms which relate the activity of Ppz1p/Hal3p complex to nonsense suppression efficiency. In this study, we used a genetic approach implicating the analysis of nonsense suppression phenotype of the strains overexpressing HAL3 or PPZ1 genes and also bearing deletions or mutant alleles of genes, which presumably could participate in the manifestation of these overexpressions. We have shown that Hal3p inhibits not only Ppz1p but also the homologous phosphatase Ppz2p. Our data indicate that Ppz2p is also involved in the control of nonsense suppression efficiency. In the course of search for Ppz1p target protein, it was shown that Ppz1p dephosphorylates at least two proteins involved in translation. Moreover, Ppz1p affects the efficiency of nonsense suppression not only due to its phosphatase activity but also due to another mechanism triggered by its interaction with Hsp70 chaperones.