Does the Epsilon Sequence of Phage T7 Function as an Initiator for the Translation of CAT mRNA inEscherichia coli?

Abstract

Epsilon (ϵ) sequence [UUAACUUUA, complementary to nucleotides 458-466 of the 16S ribosomal RNA (rRNA)] which is naturally occurring at the 5′-untranslated leader of phage T7 gene10mRNA was originally described as a powerful translational enhancer inEscherichia coli.Recent studies with this sequence led to controversial conclusions about its translational initiation and enhancing capability. In this study different sequence derivatives of ϵ were constructed to evaluate its efficiency not only to enhance translation of the chloramphenicol acetyltransferase (CAT) mRNA inE. coli,but also to function as an independent initiator of translation. It was observed that the ϵ sequence in combination with the CAT natural Shine-Dalgarno (SDn) or the SD consensus sequences enhanced, as expected, the translation of CAT mRNA. The natural ϵ sequence without an SD sequence failed to initiate or enhance the translation of CAT mRNA. However, when the complementarity of ϵ to 16S rRNA was increased from 9 to 16 nucleotides, ϵ alone (without the SD sequence) became an independent translational initiator with an efficiency of about 80% that obtained with the SD consensus sequence.