RNA polymerase and the lead ribosome may be physically linked in E. coli by the two-domain NusG protein. This will be demonstrated at the biochemical, structural and genetic levels. We intend to isolate a complex between FL NusG and the 70S ribosome, and to probe its structure using cryo-EM. We will screen a number of mutants for their effects on coupling transcription and translation. Our results indicate that RelA is required for coupling and this will be explored genetically and biochemically. Our studies have implicated tmRNA as the function that uncouples transcription and translation when translation is inhibited. Structural data indicates that tmRNA can displace NusG from the ribosome; we will test this in vitro. NMR and biochemical analyses suggest that NusA can displace NusG from RNAP. This will be tested in a purified transcription system. Chromosome integrity depends on transcription termination. The details of this reaction will be explored. Finally, we find that transcription is linked to repair of a variety of DNA damages. The influence of transcription depends on the type of DNA damage. We will explore the pathways that repair DNA DSBs, DNA adducts, and interstrand crosslinks, and that can remove tightly bound protein from the DNA template.