GE23077, a novel microbial metabolite recently isolated from Actinomadurasp. culture media, is a potent and selective inhibitor of bacterial RNApolymerase (RNAP). It inhibitsGram-positive (Bacillus subtilis) andGram-negative (Escherichia coli)RNAPs with IC50 values (. the concen-tration at which the enzyme activity is inhibited by 50%) in the 10 )8 Mrange, whereas it is not active onE. coliDNA polymerase or on eukaryotic (wheat germ) RNAP II (IC50 values10 )4 Min both cases).
