EXPRESSION OF THE MITOCHONDRIAL RNASE-P RNA SUBUNIT-ENCODING GENE FROM A VARIANT PROMOTER SEQUENCE IN SACCHAROMYCES-CEREVISIAE

Ribonuclease P (RNase P) is a common tRNA processing; enzyme that remo ves the 5' leader sequence of precursor tRNAs. This activity is identi fied in yeast mitochondria as a separate enzyme from the nuclear RNase P, Like other RNase P enzymes, the mitochondrial (mt) RNase P is also a ribonucleoprotein composed of both RNA and protein subunits. The RN A subunit is encoded by a mt gene and the protein subunit is supplied by a nuclear gene. Earlier studies described one active promoter (FP1) located 5' to the mt tRNA(fMet)-RNase P RNA-tRNA(Pro) gene cluster, s o that the mitochondrially encoded RNA subunit was thought to be co-tr anscribed with two of its substrate tRNAs. However, the results of in vitro transcription and primer extension experiments presented here de monstrate that the mt RNase P RNA subunit-encoding gene (RPM1) is tran scribed from a new promoter (SP) which is located between the tRNA(fMe t) and RPM1 genes. The sequence [5'-TATAAGAA(fl)] of the new promoter varies from the conserved promoter sequence [5'-TATAAGTA(+1)], but is one of the sequences that is active in the in vitro transcription assa y to determine the consensus promoter sequence [5'-T A T/a A A/g/c G T /a/c N(+1)], This result demonstrates that a naturally occurring varia nt promoter is used by RPM1. Identification of the novel SP promoter s uggests that the synthesis of the mt RNase P RNA subunit might be unco upled from the expression of upstream tRNA(fMet) gene, and that RPM1 m ight be independently transcribed in Saccharomyces cerevisiae.