STRUCTURAL AND COMPOSITIONAL FEATURES OF UNTRANSLATED REGIONS OF EUKARYOTIC MESSENGER-RNAS

The important role of 5' and 3' untranslated regions of eukaryotic mRN As in gene regulation and expression is now widely accepted. In order to study the general structural and compositional features of these se quences we developed UTRdb, a specialized database of 5' and 3'-UTR se quences from seven different taxonomic groups of eukaryotic mRNAs clea ned of redundancy. The analysis of the UTR sequences contained in this database showed that 5'-UTR sequences, on average 200 nucleotides lon g, are 1.5-3 times shorter than the corresponding 3'-UTR sequences in the various taxonomic groups considered here. As to their compositiona l properties on average 5'-UTR sequences resulted in all cases GC rich er than 3'-UTR sequences, and significant correlations were found betw een the GC content of 5' and 3'-UTR sequences and the GC content of th e third silent codon positions of the corresponding protein coding gen es. The dinucleotide analysis showed a differential depletion of CpG i n vertebrate 5' and 3'-UTR, with 5'-UTR sequences being more CpG-rich, and a generalized depletion of TpA in both 5' and 3'-UTR was observed in all eukaryotic sequence collections. (C) 1997 Elsevier Science B.V .