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Effects of ribosomal proteins S1, S2 and the DeaD/CsdA DEAD‐box helicase on translation of leaderless and canonical mRNAs in Escherichia coli

2002; Wiley; Volume: 44; Issue: 5 Linguagem: Inglês

10.1046/j.1365-2958.2002.02971.x

1365-2958

Isabella Moll, Sonja Grill, Angelika Gründling, Udo Bläsi,

RNA Research and Splicing

Summary Leaderless mRNAs beginning with the AUG initiating codon occur in all kingdoms of life. It has been previously reported that translation of the leaderless λcI mRNA is stimulated in an Escherichia coli rpsB mutant deficient in ribosomal protein S2. Here, we have studied this phenomenon at the molecular level by making use of an E. coli rpsB ts mutant. The analysis of the ribosomes isolated under the non‐permissive conditions revealed that in addition to ribosomal protein S2, ribosomal protein S1 was absent, demonstrating that S2 is essential for binding of S1 to the 30S ribosomal subunit. In vitro translation assays and the selective translation of a leaderless mRNA in vivo at the non‐permissive temperature corroborate and extend previous in vitro ribosome binding studies in that S1 is indeed dispensable for translation of leaderless mRNAs. The deaD/csdA gene, encoding the ‘DeaD/CsdA’ DEAD‐box helicase, has been isolated as a multicopy suppressor of rpsB ts mutations. Here, we show that expression of a plasmid borne deaD/csdA gene restores both S1 and S2 on the ribosome at the non‐permissive temperature in the rpsB ts strain, which in turn leads to suppression of the translational defect affecting canonical mRNAs. These data are discussed in terms of a model, wherein DeaD/CsdA is involved in ribosome biogenesis rather than acting directly on mRNA.