Non-canonical mechanism for translational control in bacteria: synthesis of ribosomal protein S1.

Translation initiation region (TIR) of the rpsA mRNA encoding ribosomal protein S1 is one of the most efficient in Escherichia coli despite the absence of a canonical Shine-Dalgarno-element. Its high efficiency is under strong negative autogenous control, a puzzling phenomenon as S1 has no strict sequence specificity. To define sequence and structural elements responsible for translational efficiency and autoregulation of the rpsA mRNA, a series of rpsA'-'lacZ chromosomal fusions bearing various mutations in the rpsA TIR was created and tested for beta-galactosidase activity in the absence and presence of excess S1.

Ribosome-messenger recognition in the absence of the Shine-Dalgarno interactions.

In an attempt to understand how Escherichia coli ribosomes recognize the initiator codon on mRNAs lacking the Shine-Dalgarno (SD) sequence, we have studied 30S initiation complex formation in extension inhibition (toeprinting) experiments using (-SD)mRNAs which are known to be reliably translated in E. coli: the plant viral messenger A1MV RNA 4 and two chimaeric mRNAs coding for beta-glucuronidase (GUS) and bearing the 5'-untranslated sequence of TMV RNA (omega) or the omega-derived sequence (CAA)n as 5'-leaders. Ribosomal protein S1 and IF3 have been found to be indispensable for translational initiation.

Ribosome-messenger recognition: mRNA target sites for ribosomal protein S1.

Ribosomal protein S1 is known to play an important role in translational initiation, being directly involved in recognition and binding of mRNAs by 30S ribosomal particles. Using a specially developed procedure based on efficient crosslinking of S1 to mRNA induced by UV irradiation, we have identified S1 binding sites on several phage RNAs in preinitiation complexes. Targets for S1 on Q beta and fr RNAs are localized upstream from the coat protein gene and contain oligo(U)-sequences.