Preparation of full-length TAV RNA 3 transcripts DNA templates representing a full-length RNA 3 of TAV and including T7 or T3 promoter were generated by PCR using the infectious cDNA clone of TAV RNA 3 (T3) as a template and primer pairs T3 0 and T7-TR3(+) (a primer used for transcription of the sense RNA), or T5 0 (nucleotides 1-27 of TAV RNA 3) and T3-TR3(À) (a primer used for transcription of the anti-sense RNA; see Supplementary Table 1 for the primer sequences). Labelled transcripts from the DNA templates were obtained using [ 32 P]-a-UTP and T7 or T3 DNA-dependent RNA polymerase. The free nucleotides in the transcription reaction were removed using P-30 micro Bio-Spin columns (Bio-Rad), while the DNA templates were removed by incubation with DNase I. The labelled TAV RNA 3 transcripts were purified through a 4% denaturing polyacrylamide gel and quantified by UV spectrophotometry (Beckman).