Expression of the split gene COB in yeast mtDNA : Mutational arrest in the pathway of transcript splicing.

Electrophoretic separation of mitochondrial RNA followed by hybridization with restriction fragments of mtDNA has been used to identify transcripts of the split gen COB which codes for apocytochrome b.In wild type a major transcript of 18S is detected besides a 10S RNA and a series of transcripts with electrophoretic mobilities higher than 18S. Mutations in coding sequences do not significantly alter this transcript pattern. In contrast, mutations in intervening sequences give rise to different patterns: The 18S RNA, the putative messenger for apocytochrome b, is lacking; depending on the intervening sequence affected by mutation, one or the other of the larger transcripts (23S, 24S, 32S, 34S) is accumulated instead. In most mutants a 10S RNA species is present; it has not been detected, however, in case of a small cluster of mutations which lead to the accumulation of the largest transcript (34S) observed, which most likely contains all coding and intervening sequences of the split gene COB.These results suggest a pathway of splicing.