Contextual Features of Higher Plant mRNA 5QUOTATION_MARK-Untranslated Regions

Computer analysis of nucleotide sequences of 5QUOTATION_MARK-untranslated regions (5QUOTATION_MARK-UTR) of higher plant mRNA adopted from the EMBL nucleotide sequence database was carried out. It was demonstrated that the average nucleotide frequencies of the leader sequences and adjacent regions of basal promoters are similar, whereas introns and 3QUOTATION_MARK-UTR have a higher content of T and a lower content of C. A particular 5QUOTATION_MARK-UTR contextual feature is a misbalance in the content of complementary nucleotides, probably caused by negative influence of the stable secondary structure on the translation properties of the leader sequence. Approximately 20% of 5QUOTATION_MARK-UTR possess AUG triplets, i.e., twice as much as it has been estimated earlier. The properties of the open reading frames of the leader sequence (uORF) and presumable causes of their high content in 5QUOTATION_MARK-UTR of eukaryotic mRNAs are discussed. The nature of correlation between some features of uORFs and protein-coding gene sequences is analyzed. It is demonstrated that in effectively translated mRNAs the leader AUG triplets are more frequently located in a nonoptimal context, whereas the terminating codons of uORFs more frequently exist in the optimal one. A hypothesis is put forward that the efficiency of termination at the uORF stop codon might substantially interfere with the mRNA translation activity.