Multiple polyadenylation signals and 3' untranslated sequences are conserved between chicken and human cellular myosin II transcripts.

We have isolated a chicken cellular myosin II heavy chain isoform cDNA clone that overlaps the published sequence for MHC-A (Shohet et al., 1989, Proc Natl Acad Sci 86, 7726-7730) and contains three canonical AAUAAA-polyadenylation signals in an additional 374 nucleotides at its 3' end. S1 nuclease protection analysis and PCR-amplification of MHC-A cDNA 3' ends have confirmed that all three of the signals are used in vivo. Differential usage of these signals without differential splicing in this region yields three messages that differ at their 3' ends but appear to encode the same protein. Comparison of the new chicken sequence with the homologous human MHC-A cDNA sequence (Saez et al., 1990, Proc Natl Acad Sci 87, 1164-1168) has revealed a number of similarities at this end of their long 3' untranslated regions (3'-UTRs). The three chicken polyadenylation signals reported here are positioned similarly to three signals evident in the human sequence. This region also contains distinct stretches of identity that are interspersed with regions of little homology. Within these regions of identity are a number of conserved sequence motifs, some of which have been demonstrated to be involved in mRNA metabolism in other systems. The pattern of mRNA sequence conservation demonstrated here suggests that the mechanisms for regulating MHC-A mRNA metabolism have been conserved between chickens and humans.