Localization of rRNA Synthesis in Bacillus subtilis : Characterization of Loci Involved in Transcription Focus Formation

Abstract

ABSTRACT In Bacillus subtilis , RNA polymerase becomes concentrated into regions of the nucleoid called transcription foci. With green fluorescent protein-tagged RNA polymerase, these structures are only observed at higher growth rates and have been shown to represent the sites of rRNA synthesis. There are 10 rRNA ( rrn ) operons distributed around nearly half of the chromosome. In this study we analyzed the rrn composition of transcription foci with fluorescently tagged loci and showed that they comprise the origin-proximal operon rrnO but not the more dispersed rrnE or rrnD . This suggests that transcription foci comprise only the seven origin-proximal operons rrnO , rrnA , rrnJ , rrnW , rrnI , rrnH , and rrnG . These results have important implications for our understanding of microbial chromosome structure.