Progeny RNA of CyRSV RNA transcripts ending with -GGG, instead of -CCC as in wild-type RNA, was analyzed and shown to revert to wild-type. A new full-length cDNA clone of CyRSV was prepared, bearing the correct 3′ terminus, from which transcripts could be synthesized having very high infectivity. Mutants were prepared which lacked the three terminal Cs; transcripts were infectious and most cDNA clones recovered from progeny RNA had regained the wild-type sequence. Transcripts ending in -GGCCAn were also infectious, and the 3′ sequence of most cDNA clones recovered after inoculation was the same as the inoculum sequence. Deletion of G at position -4 completely abolished infectivity. The occurrence of a repair mechanism at the 3′ end of CyRSV similar to telomerase activity on chromosomes is suggested.
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