MAKING (ANTI)SENSE OF NONCODING SEQUENCE CONSERVATION

A substantial fraction of vertebrate mRNAs contain long conserved bloc ks in their untranslated regions as well as long blocks without silent changes in their protein coding regions. These conserved blocks are l argely comprised of unique sequence within the genome, leaving us with an important puzzle regarding their function. A large body of experim ental data shows that these regions are associated with regulation of mRNA stability. Combining this information with the rapidly accumulati ng data on endogenous antisense transcripts, we propose that the conse rved sequences form long perfect duplexes with antisense transcripts. The formation of such duplexes may be essential for recognition by pos t-transcriptional regulatory systems. The conservation may then be exp lained by selection against the dominant negative effect of allelic di vergence.