Transcriptional Initiation of Yeast Mitochondrial RNA and Characterization and Synthesis of Mitochondrial RNA Polymerase

Abstract

A complete knowledge of mitochondrial gene expression demands an understanding of the events involved in the initiation, elongation, termination, and maturation of mitochondrial transcripts. Whereas many significant features of the processing of the 21S and 14S rRNAs and the cob and oxi3 transcripts have been elucidated (Church et al. 1979; Bonitz et al. 1980; Bos et al. 1980; Halbreich et al. 1980; Merten et al. 1980; Van Ommen et al. 1980), virtually nothing is known about the regulation of the synthesis of the primary transcripts for these genes. In this paper we present some of our results concerning the localization of the sites for the initiation of RNA synthesis in the mitochondrial genome. We have found multiple initiation sites in the yeast mitochondrial genome, in contrast to the situation observed in mammalian mitochondria. In addition, we describe our studies concerning the role of the mtRNA polymerase in the regulation of mitochondrial biogenesis.

Because of the extensive processing of mitochondrial transcripts and the lack of promoter mutations, the sites for the initiation of mtRNA synthesis have not been identified by conventional biochemical and genetic methods. Assuming that mitochondrial transcripts are initiated with a 5′-triphosphate nucleotide, and since there is no evidence for in vivo capping of mitochondrial transcripts, we have exploited the properties of the vaccinia virus guanylyltransferase to label transcripts retaining their original 5′ ends. This enzyme catalyzes the coupling of GTP to a polyribonucleotide terminated with a diphosphate or triphosphate (Martin and Moss 1975; Martin et al. 1975; Monroy...