The rate of transcription elongation in Escherichia coli was reduced when cells were depleted of NusG. In a purified in vitro system, NusG accelerated the transcription elongation rate. The stimulation of the rate of transcription elongation by NusG appears to result from the suppression of specific transcription pause sites.The Escherichia coli nusG gene encodes an essential transcription factor that has been implicated in a variety of cellular and viral termination and antitermination processes (2,9,10,21,22). NusG is required, along with other Nus factors, for effective antitermination by N protein of phage in vitro (2,8,10,11,15). The nusG4 mutation restores N activity in a nusA1 host, suggesting that NusG is also involved in antitermination in vivo (22). NusG has been shown to stimulate Rho-dependent termination in vivo (21).In vitro experiments indicate that NusG binds directly and selectively to Rho (9) and more weakly to core RNA polymerase (8). NusG both stimulates and changes the pattern of Rho-dependent termination at the tR1 and trp tЈ terminators (9,14). A model has been proposed in which NusG serves as a bridge between RNA polymerase and Rho, thus helping to recruit Rho into the termination complex (9). Indeed, recent evidence indicates that NusG stably associates with stalled elongation complexes only if Rho is bound to the nascent RNA and that the presence of NusG in the complex leads to a slower off-rate of Rho from the transcript (13).The participation of NusG in factor-dependent termination and antitermination processes, both of which involve modulation of transcription elongation, suggests the possibility that NusG may directly affect the rate at which RNA polymerase synthesizes RNA molecules. In this paper, we demonstrate that NusG increases the rate of transcription elongation both in vivo and in vitro. The ability of NusG to suppress transcriptional pausing probably accounts for its acceleration of the overall rate of transcription elongation.NusG depletion slows the rate of transcription elongation. We first asked if depletion of NusG affected the rate of transcription elongation in E. coli cells. Strains SS287 and SS294 are derivatives of N99 that carry a nusG::Kn chromosomal insertion and a nusG ϩ plasmid. SS287 carries the rep ts plasmid pSS119; SS294 carries the rep ϩ plasmid pSS120. Depletion of NusG in SS287 occurs when the cells are shifted from 32 to 42ЊC, inducing the loss of the pSS119 plasmid (1, 21).The rate of RNA chain growth can be estimated from the time of appearance of ␤-galactosidase after IPTG (isopropyl ␤-D-thiogalactosidase) induction of lacZ (5). This technique has been used recently to demonstrate altered rates of elongation by certain RNA polymerase mutants (3). To measure the effect of NusG depletion on the initial kinetics of ␤-galactosidase induction, SS287 and SS294 were grown in LuriaBertani medium at 32ЊC until early log phase and shifted to 42ЊC for 2.5 h. Cultures were maintained in exponential growth by dilution into fresh media. Optical density at 650 nm...

SummaryThe Escherichia coli nusG gene product is required for transcription termination by phage HK022 Nun protein at the nutR site in vivo. We show that it is also essential for Nun termination at nutL.

The Escherichia coli NusG protein binds Rho in vitro and is required for efficient Rho-dependent transcription termination in vivo. In this work we examine transcription termination in cells that over-express NusG. Termination at the Rho-dependent lambda tL1 and lambda tR1 sites was significantly inhibited by excess NusG, whereas the Rho-independent lambda tl site was fully functional. Although Western analysis showed no reduction in the levels of soluble Rho, termination was restored when Rho was also overexpressed. Our data indicated that the ratio of NusG and Rho proteins affects the efficiency of transcription termination.

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Thermal denaturation of distamicin A-DNA complexes as followed hyperchromic spectra // Biophys. Chem.-1980.-11, N 2.-P. 233-237. 11. Об особенностях перехода спираль-клубок ДНК в области инверсии относительной стабильности GC-и АТ-пар, обусловленной ионами Си 2 + и Мп 2+ / Ю.

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