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N-Utilization Substance G (NusG) N-terminal domain in the NusG Specialized Paralog (SP), UpxY The N-Utilization Substance G (NusG) proteins are involved in transcription elongation and termination. NusG is essential in Escherichia coli and is associated with RNA polymerase elongation and Rho-termination. Paralogs of eubacterial NusG, NusG SP (Specialized Paralog of NusG), are more diverse and often found as the first ORF in operons encoding secreted proteins and LPS (lipopolysaccharide) biosynthesis genes. NusG SP family members are operon-specific transcriptional antitermination factors. UpxY proteins, UpxY proteins, where the x is replaced by the letter designation of the specific polysaccharide (UpaY to UphY), are a family of NusG SP factors that act specifically in transcriptional antitermination of operons from which they are encoded. UpxYs are necessary and specific for transcription regulation of the polysaccharide biosynthesis operon. Orthologs of the NusG gene exist in all bacteria, but their functions and requirements are different. The NusG N-terminal (NGN) domain is similar in all NusG orthologs, but its C-terminal domain and the linker that separate these two domains are different. The domain organization of NusG and its orthologs suggests that the common properties of NusG and its orthologs and paralogs are due to their similar NGN domains.
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