Electron microscopic heteroduplex analysis of "killer" double-stranded RNA species from yeast.

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Abstract
Wild-type and mutant double-stranded RNA (dsRNA) species from the yeast Saccharomyces cerevisiae were studied by EM heteroduplex mapping to determine the sequence relationships among the different RNA molecules. Three mutant dsRNa, 1.5, 1.4 and 0.73 kilobase, were found to be derived by the same internal deletion of the wild-type (1.83 kilobases) molecule. This deletion includes a segment of about 200 base pairs that was estimated to be nearly 100% A + U. In addition, the sequences of the 2 larger mutant RNA species are tandem, direct duplications. One of the duplicated molecules appears to have a second internal deletion that occurred after the duplication. The mutant dsRNA are functionally similar to the defective interfering virus particles of animal viruses-all of the mutant species prevent the propagation of the wild-type dsRNA when both are present in the same cell. The 4 dsRNA share the same sequences at their termini, a finding that may suggest that these sequences are important for the replication of the dsRNA.