Poly(A) addition site mapping and polyadenylation signal analysis in a plant circovirus replication-related gene

The transcripts of a genomic component of coconut foliar decay virus (CFDV), a plant circovirus with a single-stranded DNA genome, were characterized by sequencing the 3' termini of the respective cDNA clones. It was shown that transcription of the putative replication-related gene terminated at one major site (six bases downstream of the termination codon) in electroporated barley mesophyll protoplasts and that the resulting transcripts were polyadenylated. A deletion downstream of the AATAAA sequence including the poly(A) addition site did not inhibit polyadenylation signal activity but altered the distance between the polyadenylation signal and the polyadenylation site. However, deletion of the sequences upstream of the AATAAA stretch resulted in inhibition of the polyadenylation in this region. These observations and the finding of a silent CFDV AATAAA sequence downstream of the active poly(A) signal confirm the role of the upstream elements in processing of RNA transcripts in plants.