The 5' untranslated mRNA region base content can greatly affect translation initiation in the absence of secondary structures in Prevotella bryantii TC1-1

It has become clear lately that many bacteria and even whole bacterial phyla do not use the classical Shine-Dalgarno sequence mediated pathway of protein translation initiation. The prominent phylum Bacteroidetes is one of them, and this was shown not only using bioinformatic but also functional reporter gene studies in its representative Prevotella bryantii. The latter studies revealed much higher sensitivity toward secondary structures in 5(') untranslated mRNA regions (5(') UTRs) during translation initiation compared to Escherichia coli. It was proposed that in the absence of Shine-Dalgarno sequence interaction the key elements enabling translation initiation are local absence of secondary structures in 5(') UTRs, and the ribosomal protein S1 which binds to mRNA. Here, we evaluate the 5(') UTRs devoid of secondary structures but containing divergent nucleotide compositions in P. bryantii reporter assay. We show that base composition profoundly affects the amount of the reporter synthesized, and further that these amounts were in agreement with S1 protein binding affinity for adenine/uracil bases in mRNA. This is the first, though indirect, clue that S1 is actually involved in translation initiation in Bacteroidetes and adds the second layer of control beside mRNA secondary structure affecting translation initiation in this phylum.