EXTREME HETEROGENEITY OF POLYADENYLATION SITES IN MESSENGER-RNAS ENCODING CHLOROPLAST RNA-BINDING PROTEINS IN NICOTIANA-PLUMBAGINIFOLIA

We have previously characterized nuclear cDNA clones encoding two RNA binding proteins, CP-RBP30 and CP-RBP-31, which are targeted to chloro plasts in Nicotiana plumbaginifolia. In this report we describe the an alysis of the 3'-untranslated regions (3'-UTRs) in 22 CP-RBP30 and 8 C P-RBP31 clones which reveals that mRNAs encoding both proteins have a very complex polyadenylation pattern. Fourteen distinct poly(A) sites were identified among CP-RBP30 clones and four sites among the CP-RBP3 1 clones. The authenticity of the sites was confirmed by RNase A/T1 ma pping of N. plumbaginifolia RNA. CP-RBP30 provides an extreme example of the heterogeneity known to be a feature of mRNA polyadenylation in higher plants. Using PCR we have demonstrated that CP-RBP genes in N. plumbaginifolia and N. sylvestris, in addition to the previously descr ibed introns interrupting the coding region, contain an intron located in the 3' non-coding part of the gene. In the case of the CP-RBP31, w e have identified one polyadenylation event ocurring in this intron.