Novobiocin blocks the shutoff of SPO1 early transcription

Novobiocin, an inhibitor of bacterial DNA gyrase strongly impairs the development of bacteriophage SPOl. DNA replication seems to be the primary target for the antibiotic in this system, but viral-coded transcription is also affected in several aspects: (a) The level of phage transcription is diminished; (b) the shutoff of the synthesis of early RNA classes is inhibited; (c) RNAs of late class are not synthesized. This last effect is a consequence of the coupling between transcription and replication. The other two results could be taken as an indication that the appropriate secondary structure of the parental phage DNA is a requisite for the recognition of promoters. The introduction of negative turns by DNA gyrase seems to make early genes unavailable for transcription.