Highly conserved sequencim in the 3′ untranslated region of mRNAs coding for homologous proteins in distantly related species

Canparison of the nucleotide sequence of mRNAs coding for several vertebrate actins revealed a high degree of sequence honelogy in the 3′ untranslated region (3′ UTR) between those n coding for homologous (isotypic) actins in different organisms but not between mRNAs coding for very similar isoforms differing in their function or tissue specificity. A similar pattern of sequence conservation in the 3′ UTR is also found in several other genes. Furthermore, while there is a great variation in the size of the 3′ UTR of mRNAs coding for different proteins, mRNA coding for isotypic proteins in distantly related organisms often have 3′ UTR of similar size. The data suggest that the 3′ UTR may play an important role in the regulation of expression of at least some genes at the transcriptional or posttranscriptional level.