EFFECT OF ACIDIC RIBOSOMAL PHOSPHOPROTEIN MESSENGER-RNA 5'-UNTRANSLATED REGION ON GENE-EXPRESSION AND PROTEIN ACCUMULATION

Constructions were made from genes encoding ribosomal acidic phosphopr oteins YP1 beta(L44') and YP2 beta(L45) from Saccharomyces cerevisiae in which different parts of the 5'-untransiated regions were included. The constructs were inserted into centromeric plasmids under the cont rol of the GAL1 promoter and expressed in yeast strains in which the g enes coding for each acidic protein family, P1 and P2, had been disrup ted. Deletions in the 5' region of the two genes have been found to op positely affect their expression. Deletion of most of this region stro ngly stimulates the expression of YP2 beta(L45), increasing the transl ation efficiency of the mRNA, and generating a 6-fold excess of protei n in the cell. A similar deletion in the rpYP1 beta gene represses the expression of the protein, reducing drastically the amount of the mRN A in the cell. The overexpression of rpYP2 beta affects the cell growt h by inhibiting protein synthesis at the level of initiation. Reductio n of the YP2 beta(L45) overproduction by growing in controlled concent rations of glucose abolishes the inhibitory effect. The excess protein , probably as a high molecular weight complex, apparently interferes w ith the joining of the 60 S subunit to the initiation complex generati ng the accumulation of polysome half-mers. In addition, the results in dicate the existence of a regulatory mechanism by which each one of th e two acidic proteins controls the expression of the other polypeptide . YP1 beta(L44') represses the expression of YP2 beta(L45), while this protein stimulates the expression of YP1 beta(L44').