Expression of the mitochondrial RNase P RNA subunit-encoding gene from a variant promoter sequence in Saccharomyces cerevisiae

Abstract

Ribonuclease P (RNase P) is a common tRNA processing enzyme that removes the 5' leader sequence of precursor tRNAs. This activity is identified 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 RNA 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, so that the mitochondrially encoded RNA subunit was thought to be co-transcribed with two of its substrate tRNAs. However, the results of in vitro transcription and primer extension experiments presented here demonstrate that the mt RNase P RNA subunit-encoding gene (RPM1) is transcribed from a new promoter (SP)which is located between the tRNA(fMet) and RPM1 genes. The sequence [5'-TATAAGAA(+1)] 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 assay 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 variant promoter is used by RPM1. Identification of the novel SP promoter suggests that the synthesis of the mt RNase P RNA subunit might be uncoupled from the expression of upstream tRNA(fMet) gene, and that RPM1 might be independently transcribed in Saccharomyces cerevisiae.