3'-END PROCESSING OF THE MAIZE 27-KDA ZEIN MESSENGER-RNA

Cis-regulatory elements involved in the mRNA 3'-end processing of the 27 kDa zein gene have been investigated by deletion and site-directed mutagenesis analyses. In the 3' flanking region of the 27 kDa zein gen e, several AATAAA-like sequences and a sequence resembling the mammali an GT-rich sequence are present around the polyadenylation sites. Amon g the multiple AATAAA-like sequences, the duplicated AATGAA motifs, lo cated 30-40 bp upstream from the polyadenylation sites, have been show n to play roles as polyadenylation signals. Although either of the two AATGAA motifs can function as a polyadenylation signal in chimeric ge ne constructs, the one proximal to the polyadenylation sites is likely to be the functional polyadenylation signal in the 27 kDa zein gene. Deletion of the downstream GT-rich sequence as well as alteration of t he sequence surrounding the polyadenylation sites has little effect on the mRNA 3'-end processing. However, the sequence elements located up stream from the polyadenylation signals are essential for the mRNA 3'- end processing. Mutations in the AATGAA motifs or the upstream sequenc es reduced the level of a reporter gene expression. A model depicting the mechanism involved in the 3'-end processing of the 27 kDa zein mRN A is presented.