Tomato DNA contains no detectable regions complementary to potato spindle tuber viroid as assayed by solution and...

A previous report (Hadidi et al. (1976) Proc. Nat. Acad. Sci. USA73, 2453-2457) has suggested that potato spindle tuber viroid (PSTV) RNA contains sequences complementary to the DNA of its host and, to a lesser extent, to the DNA of some nonhost species. Our studies indicate, however, that the apparent hybridization between (125)I-labeled PSTV and tomato DNA which can be observed in both solution and filter hybridization experiments is a consequence of the hybridization of host RNAs (mostly ribosomal) which are minor contaminants of the polyacrylamide gel-purified viroid preparations. When the level of these contaminants is reduced by further purification of the viroid in gels containing 8 M urea, no hybridization to tomato DNA could be detected. Thus, if sequence homology exists, it must be very minimal and its detection is beyond the capabilities of the methods employed.