3P8B:
reference: RNA polymerase and transcription elongation factor Spt4/5 complex structure., Klein BJ, Bose D, Baker KJ, Yusoff ZM, Zhang X, Murakami KS, Proc Natl Acad Sci U S A. 2011 Jan 11;108(2):546-50. Epub 2010 Dec 27. PMID: 21187417

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