Evolutionary Origin and the Biological Function of Noncoding Sequences in the Mitochondrial Genome of Yeast

Abstract

During the past 15 years we have carried out in our laboratory a series of investigations on the mitochondrial genome of Saccharomyces cerevisiae. Very early, the molecular approaches used led us to the discovery that the majority of this genome is formed by noncoding sequences. We have since concentrated our efforts on the organization of such sequences and on their biological role. In this paper I summarize what we have learned from this work and then present new results that shed some light on the evolutionary origin and the function of these sequences.

ORGANIZATION OF THE MITOCHONDRIAL GENOME OF YEAST
Sequence work performed in several laboratories during the past 3 years has confirmed our previous conclusions (for a brief review, see Bernardi 1979) on the organization of the mitochondrial genome of yeast. The majority of this genome is formed by (1) long AT stretches made up of short dAT:dAT and dA:dT sequences with rare dG:dC base pairs; AT stretches are internally repetitive in sequence and rich in palindromes (Bernardi and Bernardi 1980); and (2) short GC clusters characterized by sequences that often are symmetric and largely homologous to each other; GC clusters are embedded in AT stretches (Cosson and Tzagoloff 1979; Gaillard and Bernardi 1979). As predicted, repeated sequences within AT stretches and GC clusters are used as sites for the excision of the defective genomes of spontaneous petite mutants (Baldacci et al. 1980; Gaillard et al. 1980). Expectedly, AT stretches and GC clusters form the intergenic regions of the...