Transcription of cauliflower mosaic virus DNA. Detection of transcripts, properties, and location of the gene encoding the virus inclusion body protein.

We have detected several cauliflower mosaic virus transcripts in infected turnip leaves by northern-blot hybridization. These RNAs ranged in size from 0.9 to about 8 kb. Two species, a heterogeneous 7-to 8-kb RNA and a 2.3-kb RNA, accumulated radioactivity when CaMV-infected leaves were labeled with [32P]orthophosphate 20 days postinoculation. An abundant 62,000 MW polypeptide was synthesized in a rabbit reticulocyte lysate programmed with RNA from infected plants, but this polypeptide was absent when RNA from noninfected plants was used to direct translation. The 62,000 MW polypeptide was also the major in vitro product specified by virus-specific poly(A)+RNA purified by hybridization with CaMV DNA immobilized on DBM paper. The in vitro-synthesised 62,000 MW polypeptide was shown to be very similar to the major protein component of virus inclusion bodies by peptide fingerprint analysis. The 2.3-kb transcript is the mRNA encoding the 62,000 MW inclusion body protein. Crossed-contact hybridization mapping of this messenger on cloned CaMV DNA revealed that it is transcribed from the contiguous EcoR1 fragments d and b. The 7- to 8-kb RNA hybridized to all EcoR1 fragments and is probably a full-length primary transcript of the alpha-DNA strand.