A Comprehensive View of Mitochondrial Gene Expression in Human Cells

Abstract

In the past 2 years, the determination of the complete sequence of the human and bovine mtDNAs by Sanger’s group in Cambridge, England (see Anderson et al., this volume) has revealed the unique features of the genetic code and of the gene organization in the mammalian mitochondrial genome (Anderson et al. 1981). The parallel work carried out in our laboratory on the organization of the mtDNA transcripts in HeLa cells has produced a perfectly matching picture, providing at the same time important information on both the structure of the mitochondrial genes and their mode of expression (Ojala et al. 1980Ojala et al. 1981; Montoya et al. 1981). Thus, the extraordinarily compact gene organization of the mammalian mtDNA, with its continuous genes mostly butt-jointed to each other and a nearly complete absence of noncoding stretches, has been shown to have its precise counterpart in the tight arrangement of the mtDNA transcripts and in the distinctive structural features of the mitochondrial mRNAs. Moreover, the interspersion of the tRNA genes with the rRNA and protein-coding genes and their immediate juxtaposition have pointed to an additional functional role for tRNA sequences related to their positions in mtDNA, namely, as recognition signals for RNA processing (Attardi et al. 1980a; Ojala et al. 1981).

The information on the structural organization of the genes and their transcripts in the human mitochondrial genome has further provided the framework for an in-depth analysis of the metabolic behavior of mtRNAs in HeLa cells (Gelfand and Attardi 1981). The correlation and integration of...