JBC, Vol. 254, Issue 24, 12461-12470, Dec, 1979
Transcription, processing, and mapping of mitochondrial RNA from grande and petite yeast
R. Morimoto, J. Locker, R. M. Synenki and M. Rabinowitz
Mitochondrial RNA (mtRNA) from petite yeast strains was analyzed by
electrophoresis in agarose-urea, acrylamide-urea, and agarose-methyl
mercuric hydroxide gels, and by transfer to diazobenzyloxy-methyl paper and
hybridization to labeled mitochondrial DNA (mtDNA). Petites contain
numerous mitochondrial transcripts, including processed species like 21 S
and 14 S rRNA. Petite transcripts were found to fall into three classes: 1)
bands that comigrate with grande mtRNA species; 2) "group-specific" new
bands found in multiple strains and coinciding with specific regions of the
mitochondrial genome; and 3) "strain-specific" new bands found only in
individual petite strains. A deletion map was constructed in which we used
the presence or absence of the first two types of mtRNA bands in specific
strains, and the restriction endonuclease map of these strains. This map
confirmed the localization of 21 S and 14 S rRNA, which were mapped
previously by hybridization, and also localized more than 20 additional
mtRNA species. The mtRNA species were grouped in regions of the genome in a
fashion that strongly suggests that many of them are precursors to fully
processed mtRNA species. Hybridization experiments with grande mtRNA and
cloned mtDNA fragments have shown the same kind of transcript grouping.
Other hybridization experiments have demonstrated two apparent precursors
to 21 S rRNA (3700 nucleotides) measuring 5500 and 4500 nucleotides.
Processed tRNAs are found only in petites that contain a specific region of
the genome near the P (paromomycin resistance) locus. When this region is
absent, processed tRNAs are not detected, even for tRNA genes quite distant
from the P locus. Since this phenotype is expressed in petites that lack
mitochondrial protein synthesis, and since it maps to a specific location
in the mitochondrial genome, there appears to be a mtRNA species which has
a role in processing of mitochondrial tRNA.