Total plant RNAs were extracted from infected plants and analysed by northern blot hybridization as described previously (26) . The nylon membranes were hybridized with a 32 P-labelled transcript probe, complementary to the 3 0 terminal sequences of either TAV RNA 3 (nucleotide 2287-2386) or RNA 2 of the Q-strain of CMV (Q-CMV; nucleotide 2871-3035). These two probes would hybridize to all the genomic and subgenomic RNAs of the corresponding viruses (39) . An additional probe complementary to nucleotide 1-1884 of TAV RNA 3 was specifically used to hybridize to the 5 0 -terminal region of TAV RNA 3.