PKZ18 is an antibiotic and inhibits bacterial growth, with MIC values of 32-64 μg/mL against most Gram-positive bacteria. PKZ18 inhibits in vivo transcription and translation of glycyl-tRNA synthetase mRNA. PKZ18 selectively targets stem I specifier loops in Gram-positive bacteria and directly reduces T-box transcriptional read-through of the associated genes. PKZ18 prevents the codon-anticodon reading required for tRNA binding and is refractory to resistance.