Abstract
Formylation of the initiator methionyl-tRNA (Met-tRNA fMet) in eubacteria is catalyzed by methionyl-tRNA formyltransferase (MTF). Features of the Escherichia coli tRNA fMet that are important for formylation are the base-base mismatch between nucleotides 1 and 72, and the second and third base pairs of the acceptor stem. The base-base mismatch is the most crucial formylation determinant in the E. coli tRNA fMet. However, it is not known whether 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 catalytic properties and substrate specificity of the enzyme. The results show that the P. aeruginosa and E. coli enzymes have comparable affinities for the tRNA fMet and N 10-formyltetrahydrofolate (fTHF) substrates. Overproduction of the P. aeruginosa MTF rescued the initiator activity of an E. coli formylation-defective tRNA fMet with a base pair between nucleotides 1 and 72, indicating that the base-base mismatch is utilized by the P. aeruginosa MTF for recognition of the tRNA fMet. Therefore, this feature may be used by MTFs from other eubacteria to distinguish the initiator from elongator tRNAs.
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