Salt-inducible betaine aldehyde dehydrogenase from sugar beet: cDNA cloning and expression

In animal and viral pre-mRNAS, the process of polyadenylation is mediated through several cis-acting poly (A) signals present upstream and downstream from poly (A) sites. The situation regarding polyadenylation of higher plant pre-mRNAS, however, has remained obscure so far. In this paper, a search for putative poly (A) signals is made by considering the published data from 46 plant genomic DNA sequences. Certain domains in the 3' untranslated regions from nuclear genes of higher plants were compiled and occurrence of sequence motifs such as AATAAA, CAYTG, YGTGTTYY and YAYTG was scored in relation to poly (A) sites. Moreover, consensus sequences for important regions in the 3' untranslated sequences and poly (A) signals were also deduced from the data. It was inferred that sequence motifs similar to poly (A) signals exist around poly (A) sites but some of them are in entirely different spatial relationship than observed in other eukaryotes. This indicates their probable non-involvement in the process of polyadenylation in higher plants necessitating a functional analysis approach to define the plant specific poly (A) signals.

We have analyzed the polyadenylation sites for the small subunit of ribulose bisphosphate carboxylase and chlorophyll a/b binding protein genes of Petunia (Mitchell) and the bronze gene of Zea mays. Sequence analysis of multiple cDNA clones revealed that polyadenylation of the transcripts occurred at either 2 or 3 sites for all three groups of genes. In the examples where 3 polyadenylation sites were detected, the middle site was the one predominantly used. Putative polyadenylation signals preceding the poly A tails diverged significantly from the animal consensus sequence AATAAA. In all the genes examined the first A residue in the poly A tail of the cDNA clones corresponded to an A residue in the homologous genomic sequence.