MOVING-PICTURES AND PULSED-FIELD GEL-ELECTROPHORESIS SHOW ONLY LINEARMITOCHONDRIAL-DNA MOLECULES FROM YEASTS WITH LINEAR-MAPPING AND CIRCULAR-MAPPING MITOCHONDRIAL GENOMES

The mobility of mitochondrial DNA (mtDNA) in pulsed-field gel electrop horesis (PFGE) and its appearance in moving pictures from fluorescence microscopy were used to investigate the mitochondrial genome structur e for five Pichia and Williopsis strains of yeast. An apocytochrome b- gene hybridization probe identified only linear mtDNA molecules for ea ch strain when total cellular DNA was fractionated by PFGE. Most of th e mass of DNA isolated from mitochondria for one linear-mapping and on e circular-mapping mitochondrial genome was found in linear molecules much larger than the genome size of 50 kb; some molecules were as long as 1500 kb, but only a trace amount of apparently circular mtDNA was found for the strain with the circular-mapping genome. Probes for both the apocytochrome-b and mitochondrial small rRNA sub-unit genes hybri dized strongly to mtDNA of approximately 50-100 kb, but weakly to the larger DNA from mitochondria of these two strains. For the four linear -mapping strains, PFGE revealed two or three distinct bands of linear mtDNA, larger than the genome size, within a smear of approximately 50 -100 kb, but a smear without bands was found for the circular-mapping strain.