CHARACTERIZATION OF A 2ND NUCLEAR GENE, AEP1, REQUIRED FOR EXPRESSIONOF THE MITOCHONDRIAL OLI1 GENE IN SACCHAROMYCES-CEREVISIAE

Due to mutation in a single nuclear locus, AEP1, the temperature-condi tional pet mutant ts 1860 of Saccharomyces cerevisiae fails to synthes ize mitochondrial ATP synthase subunit 9 at the restrictive temperatur e of 36-degrees-C. The presence at this temperature of near-normal lev els of the cognate oli1 mRNA in mutant ts1860 indicates that, as previ ously shown, the product of the AEP1 gene is required for translation of the mitochondrial oli1 transcript. In this study the AEP1 gene has been cloned from a wild-type yeast genomic library by genetic compleme ntation of a temperature-conditional aep1 strain at the restrictive te mperature. A 2,330-bp genomic fragment which restores subunit 9 synthe sis in aep1 mutant strains was characterized. This fragment encoded fi ve open reading frames: the longest of these, at 1,554 nucleotides, wa s identified as the AEP1 gene, since disruption of this reading frame generated a non-conditional pet strain unable to synthesize subunit 9. The predicted product of AEP1 is a basic, hydrophilic protein of 59,5 71 Da which possesses a putative mitochondrial address sequence. Hybri dization studies with AEP1-specific probes indicate that the gene is l ocated on chromosome XIII and produces several poly(A)+ transcripts ra nging in size from 0.9 to 2.7 kb. None of the identified reading frame s share significant homologies with entries of several data bases.