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N-Utilization Substance G (NusG) N-terminal (NGN) domain Superfamily The N-Utilization Substance G (NusG) and its eukaryotic homolog Spt5 are involved in transcription elongation and termination. NusG contains an NGN domain at its N-terminus and Kyrpides Ouzounis and Woese (KOW) repeats at its C-terminus in bacteria and archaea. The eukaryotic ortholog, Spt5, is a large protein composed of an acidic N-terminus, an NGN domain, and multiple KOW motifs at its C-terminus. Spt5 forms a Spt4-Spt5 complex that is an essential RNA Polymerase II elongation factor. NusG was originally discovered as an N-dependent antitermination enhancing activity in Escherichia coli and has a variety of functions, such as being involved in RNA polymerase elongation and Rho-termination in bacteria. Orthologs of the NusG gene exist in all bacteria, but its functions and requirements are different. The diverse activities suggest that, after diverging from a common ancestor, NusG proteins became specialized in different bacteria.
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