Mechanisms of action of RNA polymerase-binding transcription factors that do not bind to DNA

The mechanism of the regulation of gene expression, a constantly expanding area of research, has been studied. DNA-dependent RNA polymerase is the enzyme of transcription, the first stage of gene expression, and a major target of regulation. (Most transcription factors interact with DNA). A class of transcription factors, including the prokaryotic proteins GreA, GreB, Gfh1, Rnk, DksA, and TraR and eukaryotic TFIIS, that do not bind DNA but directly interact wth RNA polymerase have been considered. Upon binding to RNAP polymerase, these factors reach out to the RNA polymerase catalitic center through the enzyme secondary channel and modulte the catalytic center activity. GreA, GreB, and TFIIS act by stimulating the intrinsic endonucleolytic cleavage activity of RNA polymerase catalytic center. This activity promotes RNA polymerase read-through through transcription pauses and arrest sites. The biochemical activities of other factors of these class are less clear. In this work, the data that accumulated during the last 15 years of research on this exciting group of factors are reviewed.