Regulation of mRNA formation in plants: lessons from the cauliflower mosaic virus transcription signals
The cauliflower mosaic virus (CaMV) transcription signals are common tools of plant molecular biologists. In this article, the transcription signals are discussed in light of the life cycle of CaMV, a plant pararetrovirus. Production of mature 35S RNA, the terminally redundant genomic RNA, is regulated by the 35S promoter, a very strong promoter, and by the polyadenylation signal that is present twice on the RNA but recognized only at its 3′ end. Dissection of the promoter has identified several organ-specific elements acting in concert to express the 35S RNA in most plant cells. Studies on the polyadenylation signal have revealed upstream elements inducing recognition of the AATAAA sequence and have led to the proposal that the conditional recognition of this signal is dependent on its distance from the promoter. Comparison of the CaMV signals with other plant signals allows speculation on the plant transcriptional machinery and on some striking resemblances and differences to the animal and yeast systems. Finally, potential applications of this knowledge will be described such as the construction of hybrid plant promoters or polyadenylation signals using the 35S minimal elements. Key words: cauliflower mosaic virus, 35S promoter, polyadenylation signal, 35S RNA, transcription, retroviruses.