title: Elongation factor Tu resistant to kirromycin in an Escherichia coli mutant altered in both tuf genes.
abstract: A mutant of Escherichia coli is described that displays kirromycin resistance in a cell-free system by virtue of an altered elongation factor Tu (EF-Tu). In poly(U)-directed poly(Phe) synthesis the kirromycin resistance of the crystallized enzyme ranged between a factor of 80 and 700, depending on temperature. Similarly, kirromycin-induced EF-Tu GTPase activity uncoupled from ribosomes and aminoacyl-tRNA required correspondingly higher concentrations of the antibiotic. Resistance of EF-Tu to kirromycin is a consequence of a modified enzyme structure as indicated by its altered fingerprint pattern.P1 transduction experiments showed that the kirromycin-resistant EF-Tu is coded by an altered tufB gene (tufB1). The known existence of two genes coding for EF-Tu would interfere with the recognition of a mutant altered in only one of those genes, if the mutation were recessive. Because kirromycin blocks EF-Tu release from the ribosome, kirromycin sensitivity is dominant, as shown by the failure of a mixed EF-Tu population to express resistance in vitro. Therefore, phenotypic expression of kirromycin resistance in vivo appears to be only possible if the EF-Tu mutant lacks an active tufA gene, a property likely to be inherited from the parental D22 strain. The observations that introduction of a tufA(+) region makes the resistant strain sensitive to the antibiotic and that transduction of tufB1 into a recipient other than E. coli D22 yields kirromycin-sensitive progeny support these conclusions.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002474:Cell-Free System; D002876:Chromosomes, Bacterial / Q000378:metabolism; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000235:genetics* / Q000648:ultrastructure; D005796:Genes; D009154:Mutation; D010445:Peptide Elongation Factors / Q000235:genetics*; D011728:Pyridones
chemical_list: D000900:Anti-Bacterial Agents; D010445:Peptide Elongation Factors; D011728:Pyridones; C008536:mocimycin