Recognition of the initiator tRNA by the Pseudomonas aeruginosa methionyl-tRNA formyltransferase: importance of the base-base mismatch at the end of the acceptor stent

Formylalion of the initiator methionyl-tRNA (Met-tRNA(fMet)) in eubacteria is catalyzed by methionyl-tRNA formyltransferase (MTF). Features of the Esc herichia coil tRNA(fMet) that are important for formylation are the base-ba se mismatch between nucleotides 1 and 72, and the second and third base pai rs of the acceptor stem. The base-base mismatch is the most crucial formyla tion determinant in the E. coil tRNA(fMet). However, it is not known whethe r this feature is also important for formylation of other eubacterial tRNA( fMet). We cloned the Pseudomonas aeruginosa MTF gene by complementation of an E. coli MTF mutant strain with a genomic library, and investigated the c atalytic properties and substrate specificity of the enzyme. The results sh ow that the P. aeruginosa and E, coli enzymes have comparable affinities fo r the tRNA(fMet) and N-10-formyltetrahydrofolate (fTHF) substrates. Overpro duction of the P. aeruginosa MTF rescued the initiator activity of an E. co li formylation-defective tRNA(fMet) with a base pair between nucleotides 1 and 72, indicating that the base-base mismatch is utilized by the P. aerugi nosa MTF for recognition of the tRNA(fMet). Therefore, this feature may be used by MTFs from other eubacteria to distinguish the initiator from elonga tor tRNAs. (C) 1999 Federation of European Microbiological Societies. Publi shed by Elsevier Science B.V. All rights reserved.