Polyriboadenylate synthesizing activity in chromatin of wheat seedlings

Plant mRNA 3'-end formation

Our understanding of how the 3' ends of mRNAs are formed in plants is rudimentary compared to what we know about this process in other eukaryotes. The salient features of plant pre-mRNAs that signal cleavage and polyadenylation remain obscure, and the biochemical mechanism is as yet wholly uncharacterized. Nevertheless, despite the lack of universally conserved cis-acting motifs, a common underlying architecture is emerging from functional analyses of plant poly(A) signals, allowing meaningful comparison with components of poly(A) signals in other eukaryotes. A plant poly(A) signal consists of one or more near-upstream elements (NUE), each directing processing at a poly(A) site a short distance downstream of it, and an extensive far-upstream element (FUE) that enhances processing efficiency at all sites. By analogy with other systems, a model for a plant 3'-end processing complex can be proposed. Plant poly(A) polymerases have been isolated and partially characterised. These, together with hints that some processing factors are conserved in different organisms, opens promising avenues toward initial characterisation of the trans-acting factors involved in 3'-end formation of mRNAs in higher plants.

Gibberellic acid causes increased synthesis of RNA which contains poly(A) in barley aleurone tissue

Incubation of isolated barley aleurone layers with gibberellic acid for 16 hr caused a 50% increase in the synthesis of RNA that contains poly(A) sequences [poly(A)-RNA], but had no measurable effect on the syntheses of the major RNA species. The syntheses of both the poly(A) and the heteropolymeric fractions of the poly(A)-RNA were increased. The poly(A) sequences were separated into two classes by size, one containing an average of 250 nucleotides and the other about 70 nucleotides. The two classes occurred in a molar ratio of about 1:1. Gibberellic acid increased the syntheses of both sequences to the same extent. We interpret these results to mean that gibberellic acid increases specifically the synthesis of mRNA in this tissue.