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var1 Determinant Region of Yeast Mitochondrial DNA

Ronald A. Butow, Frances Farrelly, H. Peter Zassenhaus, Michael E. S. Hudspeth, Lawrence I. Grossman, Philip S. Perlman


var1 polypeptide is a yeast mitochondrial translation product recently shown by us (Terpstra and Butow 1979; Terpstra et al. 1979) and independently by Groot et al. (1979) to be a protein associated with the 38S mitochondrial ribosomal subunit. An unusual property of var1 is the extraordinary number of different, strain-dependent electrophoretic species detected on SDS-polyacrylamide gels (Douglas and Butow 1976; Strausberg and Butow 1981). Although the biological significance of this polymorphism is unclear (we have been able to detect no other phenotypic differences between strains making different forms of the var1 protein), the marked diversity of var1 species has enabled us to probe aspects of mitochondrial gene regulation and recombination without the imposition of any particular selective condition on mitochondrial function.

Since the strain-specified apparent molecular weight of var1 does not change after many generations of vegetative growth, we have been able to use the protein polymorphism as a genetic marker to locate a region of the mitochondrial genome about 1.8 kb long between ery and oli1 (Perlman et al. 1977), termed the var1 determinant locus, which specifies the apparent molecular weight of var1 polypeptide. We have studied the genetic, physical, and biochemical properties of a number of alleles of this locus. DNA sequencing of these alleles, together with analysis of transcripts with sequence homology to var1 and physical mapping of DNA elements correlating with genetic determinants ascribed to different forms of the var1 protein, suggest that the var1 determinant region is not a complete coding sequence for the protein.

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