ASSOCIATION OF TRANSCRIPTS FROM A GROUP-I INTRON-CONTAINING GENE WITHHIGH SEDIMENTATION COEFFICIENT PARTICLES

The mitochondrial gene coding for the large rRNA contains a self-splic ing optional group-I intron (Sc-LSU.1) in some Saccharomyces cerevisia e strains, Although the mechanisms of splicing have been extensively s tudied, little is known about the possible interactions of this intron with other mitochondrial molecules such as proteins. Using glycerol g radients, we have compared the sedimentation coefficients of mitochond rial transcripts containing the Sc-LSU.1 intron in native yeast extrac ts and in purified RNA preparations. By comparing extracts from rho(+) and rho(-) cells we have found that at least three RNA species contai ning the Sc-LSU.1 intron (4.5 kb, 2.7 kb and 1.2 kb respectively) are associated in vivo with a multimolecular complex of sedimentation coef ficient 50S made up of nuclearly encoded proteins. Another RNA species of 2.7 kb, which may correspond to a cleavage at the dodecamer sequen ce of the intron, is not associated with the same particle. The possib ility that the 50S particle corresponds to the mitochondrial ribosome or its precursor form(s) is discussed.