Rapid formylation of the cellular initiator tRNA population makes a crucial contribution to its exclusive participation at the step of initiation. Issue 4 (4th January 2019)

• Record Type: Journal Article
• Authors: Shah, Riyaz Ahmad; Varada, Rajagopal; Sah, Shivjee; Shetty, Sunil; Lahry, Kuldeep; Singh, Sudhir; Varshney, Umesh
• Is Part Of: Nucleic acids research. Volume 47:Issue 4(2019)
• Page Start: 1908
• Page End: 1919
• Publication Date: 2019-01-04
• Subjects: Nucleic acids -- Periodicals; Molecular biology -- Periodicals; 572.805
• DOI: 10.1093/nar/gky1310
• Languages: English
• ISSNs: 0305-1048

Abstract

Abstract: Initiator tRNAs (i-tRNAs) possess highly conserved three consecutive GC base pairs (GC/GC/GC, 3GC pairs) in their anticodon stems. Additionally, in bacteria and eukaryotic organelles, the amino acid attached to i-tRNA is formylated by Fmt to facilitate its targeting to 30S ribosomes. Mutations in GC/GC/GC to UA/CG/AU in i-tRNACUA/ 3GC do not affect its formylation. However, the i-tRNACUA/ 3GC is non-functional in initiation. Here, we characterised an Escherichia coli strain possessing an amber mutation in its fmt gene ( fmt am274 ), which affords initiation with i-tRNACUA/ 3GC . Replacement of fmt with fmt am274 in the parent strain results in production of truncated Fmt, accumulation of unformylated i-tRNA, and a slow growth phenotype. Introduction of i-tRNACUA/ 3GC into the fmt am274 strain restores accumulation of formylated i-tRNAs and rescues the growth defect of the strain. We show that i-tRNACUA/ 3GC causes a low level suppression of am274 in fmt am274 . Low levels of cellular Fmt lead to compromised efficiency of formylation of i-tRNAs, which in turn results in distribution of the charged i-tRNAs between IF2 and EF-Tu allowing the plasmid borne i-tRNACUA/ 3GC to function at both the initiation and elongation steps. We show that a speedy formylation of i-tRNA population is crucial for its preferential binding (and preventing other tRNAs) into the P-site.