CLONING AND ANALYSIS OF THE NUCLEAR GENE MRP-S9 ENCODING MITOCHONDRIAL RIBOSOMAL-PROTEIN S9 OF SACCHAROMYCES-CEREVISIAE

The Saccharomyces cerevisiae nuclear gene MRP-S9 was identified as par t of the European effort in sequencing chromosome II. MRP-S9 encodes f or a hydrophilic and basic protein of 278 amino acids with a molecular mass of 32 kDa. The C-terminal part (aa 153-278) of the MRP-S9 protei n exhibits significant sequence similarity to members of the eubacteri al and chloroplast S9 ribosomal-protein family. Cells disrupted in the chromosomal copy of MRP-S9 were unable to respire and displayed a cha racteristic phenotype of mutants with defects in mitochondrial protein synthesis as indicated by a loss of cytochrome c oxidase activity. Ad ditionally, no activities of the gluconeogenetic enzymes, fructose-1,6 -bisphosphatase and phosphoenolpyruvate carboxykinase, could be observ ed under conditions of glucose de-repression. The respiration-deficien t phenotype could not be restored by transformation of the disruption strain with a wild-type copy of MRP-S9, indicating that MRP-S9 disrupt ion led to rho(-) or rho(0) cells. Sequence similarities of MRP-S9 to other members of the ribosomal S9-protein family and the phenotype of disrupted cells are consistent with an essential role of MRP-S9 is ass embly and/or function of the 30s subunit of yeast mitochondrial riboso mes.