Differential Impact of Random GC Tetrad Binding and Chromatin Events on Transcriptional Inhibition by Olivomycin A

Olivomycin A (OA), an antibiotic of the aureolic acid family, interferes with gene transcription upon forming complexes with GC-rich regions in the DNA minor groove. We demonstrate that the mechanism of transcriptional deregulation is not limited to OA interaction with GC-containing binding sites for transcription factors. Using electrophoretic mobility shift assays and DNAse I footprinting of cytomegalovirus (CMV) promoter fragments carrying OA-preferred GC tetrads (CMVwt), we showed OA binding specifically to GC islands. Replacement of G for A in these tetrads (CMVmut) abrogated OA binding. Furthermore, OA decreased RNA polymerase II (RNAPII) binding to the CMVwt promoter and inhibited the reporter gene expression. In line with the absence of OA binding sites in CMVmut DNA, the expression driven from this promoter was weakly sensitive to OA. In the endogenous genes OA decreased RNAPII on promoters and coding regions. In certain cases this phenomenon was concomitant with the increased histone 3 abundance. However, the sensitivity to OA did not correlate with GC patterns around transcription start sites, suggesting that certain GC stretches play unequal roles in OA-induced transcriptional perturbations. Thus, OA affects transcription via complex mechanisms in which GC tetranucleotide binding causes RNAPII/chromatin alterations differentially manifested in individual gene contexts.