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Ribosomal Protein S1: An Important Trans-Translational Factor

Iwona K. Wower, Nusrat Jahan, Christian Zwieb and Jacek Wower

S1 is an essential protein in Escherichia coli. Although not present in all bacteria, its importance for the initiation and elongation stages of protein synthesis is well established. Beside its roles as a ribosomal protein, S1 promotes transcriptional cycling, regulates bacteriophage T4 gene expression, forms a complex with the phage. λ protein β involved in recombination, and is a subunit of the fr and Qβ RNA bacteriophage replicases. Protein S1 was also shown to bind to tmRNA, an essential component of trans-translation. Although the physiological significance of protein S1 for trans-translation has been debated for many years, recent studies clearly demonstrate that protein S1 constitutes an important, yet poorly understood component of trans-translation. We show that binding of protein S1 to the free tmRNA is a prerequisite for the association between tmRNA and stalled ribosome. S1 transits the ribosome together with the tmRNA as defective proteins are targeted for proteolysis. These findings establish protein S1 as an important target for pharmacological intervention.