The sequence and secondary structure of the 3 '-UTR affect 3 '-end maturation, RNA accumulation, and translation in tobacco chloroplasts

RNA maturation and modulation of RNA stability play important roles in chlo roplast gene expression. In vitro and in vivo studies have shown that both the 5'- and 3'-untranslated regions (UTRs) contain sequence and structural elements that guide these processes, and interact with specific proteins. W e have previously characterized the spinach chloroplast petD 3'-UTR in deta il by in vitro approaches. This stem-loop forming sequence is a weak termin ator but is required for RNA maturation and also exhibits sequence-specific protein binding. To test petD 3'-UTR function in vivo, tobacco chloroplast transformants were generated containing uidA reporter genes flanked by var iants of the petD 3'-UTR, including one which does not form an RNA-protein complex in vitro, and one which lacks a stem-loop structure. Analysis of ui dA mRNA indicated that a stable secondary structure is required to accumula te a discrete mRNA, and that changes in the 3'-UTR sequence which affect pr otein binding in vitro can also affect RNA metabolism in vivo. The 3'-UTR a lso influenced beta -glucuronidase protein accumulation, but not in proport ion to RNA levels. These results raise the possibility that in tobacco chlo roplasts, the 3'-UTR may influence translational yield.