Expression of the Mouse Mitochondrial DNA Genome

Abstract

The mouse mitochondrial genome is a 16,295-bp closed circular DNA that has proved to be a model system for studies of mtDNA replication (Bogenhagen et al. 1979Bogenhagen et al. 1981; Gillum and Clayton 1979; Martens and Clayton 1979). The combined approaches of nuclease-S1 mapping (Battey and Clayton 1978) and DNA and RNA sequencing (Van Etten et al. 1980) have provided an overall model of gene expression for this genome. The hallmark of mammalian mtDNA organization is the extreme economy of DNA sequence usage. We report here some basic features of gene organization for mouse mtDNA, with special emphasis on the structural features of the tRNA genes and unique sequence properties of the two origins of replication. An examination of the detectable transcripts reveals a transcript homolog to all predicted RNA genes and protein-coding sequences, with the exception of an extended open reading frame encoded in the L strand. mtRNA isolated from mouse LD cells, an L-cell line in which the genome exists as a head-to-tail unicircular dimer (Bogenhagen et al. 1981), contains no identifiable transcripts not present in other mouse L cells with monomeric genomes. mtRNAs isolated from mouse liver and kidney tissue also consist of a population thus far indistinguishable from that obtained from L-cell tissue-culture lines.

DISCUSSION
Structure of the Mouse mtDNA Genome
Genomic Organization
The complete DNA sequence of the 16,295-bp mouse L-cell mtDNA genome has recently been determined (Bibb et al. 1981). A schematic representation of the organization of the genome is shown in Figure 1. The origin...