Identification and in vivo expression of a prokaryotic-like ribosome recognition sequence upstream of the coat protein gene of potato virus X

Conserved prokaryotic sequence motifs, distinct from the classic Shine-Dalgarno sequence, yet possessing homology to 16S rRNA in E. coli have been identified in a number of plant viruses. In this report, a similar Shine-Dalgarno-like motif located immediately upstream to the CP gene of potato virus X (PVX) was demonstrated to enable expression of a reporter gene in E. coli to approximately one third the level of a similar construct containing the classical Shine-Dalgarno sequence. Both PVX-specific CP and RNA transcripts were detected in chloroplasts purified from transgenic potato plants containing the PVX CP gene and corresponding leader sequence. Protoplasts generated from these transgenic plants were used to demonstrate that expression of the PVX CP from chloroplasts is possible. The implications of these results on the PVX infection cycle are discussed.