Rho+ factor

Rho-dependent termination requires participation of rho factor. This protein binds to the newly formed RNA and moves toward the RNA polymerase that has paused at a termination site. Rho then displaces RNA polymerase from the 3 end of the RNA. 

Termination of transcription Stem and loop + UUUUU Stem and loop + rho factor Not well characterized... 

Termination of transcription occurs when RNA pol traverses a termination signal, and this process may require the cooperation of p (rho) factor. 

Termination The process of elongation of the RNA chain contrv ues until a termination signal is reached. An additional protein, p (rho) factor, may be required for the release of the RNA product (p-dependent termination). Alternatively, the tetrameric RNA polymerase can, in some instances, recognize termination regions on the DNA template (p-independent termination). 

Rho and other termination factors. Termination proteins can also react with specific regions of DNA or of an RNA transcript to terminate transcription.183 The best known termination factor is the rho protein a hexamer of 45-kDa subunits. It interacts with transcripts at specific termination sequences, which are often C-rich, and in a process accompanied by hydrolysis of ATP causes release of both RNA and the polymerase from the DNA.192193 Additional E. coli proteins, products of genes nus A and nus G, cooperate with the rho factor at some termination sequences.194-196c The rho hexamer is a helicase that moves along the RNA transcript in the 5 —> 3 direction driven by ATP hydrolysis. If it locates an appropriate termination signal, it may utilize its helicase activity to uncoil the DNA-RNA hybrid segment within the transcription bubble (Fig. 28-4).197 198b... 

Rho factor. A protein involved in the termination of transcription of some messenger RNAs. 

Schneider, D., Gold, L. and Platt, T. (1993) Selective enrichment of RNA species for tight binding to Escherichia coli rho factor. FASEB J., 7, 201-207. 

Termination of transcription in vitro is classified as to its dependence on the protein factor, rho (p). Rho-independent terminators have a characteristic structure, which features (a) A strong G-C rich stem and loop, (b) a sequence of 4-6 U residues in the RNA, which are transcribed from a corresponding stretch of As in the template. Rho-factor-depen-dent terminators are less well defined, as shown in Figure 10-8. 

Rho factor A protein that recognizes terminator regions. 

B.R. Burgess and J.P. Richardson. 2001. RNA passes through the hole of the protein hexamer in the complex with Escherichia coli Rho factor J. Biol. Chem. TIC. 4182-4189. (PubMed)... 

This mechanism enables a length of RNA to be produced as a copy of the genetic material, the DNA, which corresponds to the protein which is ultimately required. However, not only must the RNA polymerase have a means of recognizing where to start synthesizing RNA on the DNA chain, it must also know where to stop when the appropriate length of DNA has been transcribed. The factors which ensure that RNA synthesis stops are not fully understood a protein described simply as the rho factor is involved. The length of newly synthesized m-RNA is released from the DNA chain and the DNA double helix re-forms. 

Rho factor attaches to a recognition site on mRNA and moves it along behind RNA polymerase. 

When RNA polymerase pauses at the termination site, rho factor unwinds the DNA RNA hybrid in the transcription bubble... 

FIGURE 11.7 The rho-factor mechanism of transcription termination. Rho (p) factor (a) attaches to a recognition site on mRNA and (b) moves along it behind RNA polymerase, (c) When RNA polymerase pauses at the termination site, rho factor unwinds the DNArRNA hybrid in the transcription bubble, releasing the nascent mRNA (d). 

RNA polymerase. There may be specific polymerases that act on special stretches of DNA. One polymerase may differ from another in a sigma factor (one protein component of the polymerase). There may also be a rho factor to signal the end of transcription. 

Figure 10.29 Effect of Rho factor on sedimentation rate of the synthesized RNA. The solid line represents RNA made with PHI UTP, while the dashed line represents RNA made with l CI UTP.

In yeast, the correlation between the Rho factor and MDNA is evident, the major arguments being (a) that cytoplasmic mutants (Rho mutated to Rho ) carry an altered MDNA (b) that the wild type MDNA, which is never lost even upon the complete disintegration of the mitochondrial organelle under repressed anaerobic conditions, is extensively transcribed into RNAs (as tested by specific hybridization (Fukuhara)) under derepressed aerobic conditions, i.e. when the respiratory activity develops and the characteristic mitochondrial structures are elaborated. 

In some strains of yeast, mutation to chloramphenicol and tetracycline resistance are associated with a decreased permealnlity of the cell-memln ane, while in the same strains mutation to macrolide (oythromydn) resistance is expressed as a change in the sensitivity of the mitochondrial protein-synthesizing system itself. For the same cell, erythromycin resistance was also shown to be extrachromosomi-cally inherited, and the corresponding genetic factor related to the mitochondrial Rho factor. The synthesis of yeast mitochondrial ribosomes seons to be (at least partly) under the control of the mitochondrial goietic determinant MDNA. 

A number of enzymes which bind polyanions such as DNA may be separated broadly into those which recognize special sequences with higher affinity than "bulk DNA" and those which bind nonspecifically. The first group includes RNA polymerases, repressors, cAMP receptor protein (CRP), the rho factor, restriction endonucleases, and methy-lases the second group includes histones and DNA-unwinding proteins. 

---