TYLCV C3 and TGMV AL3 are functional homologs. (A) The entire genome of TYLCV and the replication-competent A component of TGMV are shown. TYLCV is a 2.8-kb DNA with six open reading frames, while TGMV A is a 2.5-kb DNA with five open reading frames (arrows). Both DNAs have a 5′ intergenic region (white box), which contains the rolling circle replication origin. (B) A linear diagram of TYLCV or TGMV A complementary sense open reading frames shows the region deleted in the ΔC3 and ΔAL3 replicons. (C) Tobacco protoplasts were electroporated with the indicated replicon and expression cassette, and double-stranded and single-stranded viral DNA accumulation were monitored and quantified on DNA gel blots at 72 h posttransfection by phosphorimage analysis. The replicons were wild-type TYLCV (TY, lane 1), ΔC3 (lanes 2 to 4), wild-type TGMV A (TG, lane 5), and ΔAL3 (lanes 6 to 8). The expression cassettes were an empty 35S cassette (lanes 1, 2, 5, and 6), a TYLCV C3 cassette (lanes 3 and 8), and a TGMV AL3 cassette (lanes 4 and 7).