Structure and 5'-termini of the large and 19 S RNA transcripts encoded by the cauliflower mosaic virus genome

Cauliflower mosaic virus-infected leaves accumulate two major RNA species late in infection-a 19 S RNA and a large RNA transcript. We have found that the large transcript is approximately full genome length. The 3'-end of the large transcript is located at or near a site corresponding to the 3'-end of the 19 S RNA. The 5'-end of the large transcript maps near its own 3'-end and only about 100 bp downstream from the terminator codon for coding region VI. The 5'-end of the large transcript is situated at the beginning of the large intergenic region, about 600 bp upstream from the single-strand break in the transcribed viral DNA strand. The location of this site is of particular interest because it suggests that synthesis of the large transcript proceeds across the DNA break site. The 5'-end of the 19 S RNA maps in the small intergenic region between coding regions V and VI about 20-30 bp upstream from the initiation codon for coding region VI. By comparing the transcription initiation sites to DNA sequences for the CaMV genome, it can be shown that TATATAA sequences lie 20-30 bp upstream from the 5'-ends of both the 19 S and large transcripts.