Alternative polyadenylation generates three low-pI alpha-amylase mRNAs with differential expression in barley

Specific low-pI alpha-amylase genes from barley (Hordeum vulgare L.) produced alternative mRNAs with a 17-base 3' extension (extension 1) or a 17-base extension beyond this (extension 2). The extended mRNAs do not arise from splicing of downstream sequences, and not all low-pI genes contain the extended sequences. All three mRNAs occur in aleurones and shoots, while extension 2 is missing from scutella. Also, the unextended mRNAs predominate in total mRNA, but the extended mRNAs predominate in membrane-bound polysomes. The extended sequences do not occur in previously characterized alpha-amylases, but 16 of 18 bases, mainly in extension 1, are identical with a sequence in the 3'-UTR of PAPI, a putative inhibitor of alpha-amylase. These observations suggest that the extended sequences could play a functional role in alpha-amylase expression.