Poly(A)-Associated RNA from the Mitochondrial Fraction of the Fungus Trichoderma

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Abstract
Total RNA was extracted from purified mitochondrial and cytoplasmic fractions of germinating conidia of T. viride and bound to oligo(dT)-cellulose at 22 and 4.degree. C. Under chromatographic conditions which retained very short poly(A) segments (i.e., 4.degree. C), up to 10% of short-term 32PO4-labeled RNA from the mitochondrial fraction were selectively bound. The poly(A)-associated RNAs from the mitochondrial and cytoplasmic fractions showed the following characteristics. On polyacrylamide gels, mitochondrial fraction RNA had a distinctive pattern with a major peak at about 22 S and a smaller one at about 29 S; in contrast, cytoplasmic fraction RNA was heterogeneously distributed along the gel. The poly(A) segment released by RNase digestion of mitochondrial fraction poly(A)-associated RNA migrated on polyacrylamide gels as molecules 20-25-nucleotides long, while that of the cytoplasmic fraction showed an apparent size of 50-60 nucleotides. Mitochondrial fraction RNA bound to oligo(dT)-cellulose in the cold had a guanine + cytosine content of 21% vs. 34% for bulk mitochondrial RNA and 48% for cytoplasmic poly(A)-associated RNA; the oligo(dT)-bound RNAs were further identified by their high percentages of adenine residues (46% for the mitochondria and 30% for the cytoplasm). The poly(A)-associated RNA fraction was translated, in vitro, in a cell-free protein-synthesizing system from wheat germ. The products induced by cytoplasmic RNA showed a complex pattern on polyacrylamide gels of many polypeptides ranging in MW from about 10,000 to 40,000. The pattern induced by mitochondrial fraction RNA however, was much simpler, revealing 2 discrete, main products: a major one at Mr .apprxeq. 13,000 and a minor one at Mr .apprxeq. 20,000.