Ribosomal protein S1 promotes transcriptional cycling

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Abstract
Prokaryotic RNA polymerases are capable of efficient, continuous synthesis of RNA in vivo, yet purified polymerase-DNA model systems for RNA synthesis typically produce only a limited number of catalytic turnovers. Here, we report that the ribosomal protein S1—which plays critical roles in translation initiation and elongation in Escherichia coli and is believed to stabilize mRNA on the ribosome—is a potent activator of transcriptional cycling in vitro. Deletion of the two C-terminal RNA-binding modules—out of a total of six loosely homologous RNA-binding modules present in S1—resulted in a near-loss of the ability of S1 to enhance transcription, whereas disruption of the very last C-terminal RNA-binding module had only a mild effect. We propose that, in vivo, cooperative interaction of multiple RNA-binding modules in S1 may enhance the transcript release from RNA polymerase, alleviating its inhibitory effect and enabling the core enzyme for continuous reinitiation of transcription.