Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The N protein of bacteriophage lambda (N lambda) modifies Escherichia coli RNA polymerase in such a way that it transcribes through termination signals, a process called antitermination. N antitermination normally occurs only if the template contains a specific utilization or nut site upstream of the terminators and only in the presence of host-encoded Nus proteins. The lambda-related phages 21 and P22 produce N analogs, N21 and N22, but these require different nut sites and show a different pattern of functional interaction with one of the Nus factors, NusA, according to whether this protein is of E. coli or Salmonella origin (NusAEc or NusASal). We report the overproduction of N lambda, N21, or N22, each of which was induced by isopropyl-beta-D-thiogalactopyranoside at 37 degrees C from its cloned position downstream from ptac on a high-expression plasmid, each in a host that provided NusAEc or NusASal. Overproduction of each of these N proteins resulted in relaxed specificity for nut, which was shown by the ability to complement N mutants of heterologous phages; NusA specificity was determined by the N type that was present in these complementation tests. We also observed that excess N was able to suppress transcriptional polarity in the particular case of cloned 'trpA, the last gene of the tryptophan operon, although there was no effect on polarity within chromosomal trpE. Such polarity is attributed to the presence of cryptic intragenic terminators that become exposed in the absence of translation. Because there is no known nut site cis to 'trpA, we suggest that the 'trpA segment itself fortuitously contains a nut sequence that is able to function with excess N of any of the types tested and with either NusAEc or NusASal. We also found that excess N of any specificity, or even inactive N with missense mutation, could cause an increase in the level of NusAEc or NusASal, possibly because interaction between N and NusA, but independent of nut, whether functional or not, interferes with the autoregulation of NusA synthesis. These observations highlight the importance of protein concentration for the specificity of interactions both with other proteins and with nucleic acids. They also indicate that the interaction between N and NusA requires nut participation both for specificity and functionality.
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PMID:Overexpression of N antitermination proteins of bacteriophages lambda, 21, and P22: loss of N protein specificity. 265 5

A mutation is described that alters the promoter specificity of sigma 70, the primary sigma factor of Escherichia coli RNA polymerase. In strains carrying both the mutant and wild-type sigma gene (rpoD), the mutant sigma causes a large increase in the activity of mutant P22 ant promoters with A.T or C.G instead of the wild-type, consensus G.C base-pair at position -33, the third position of the consensus -35 hexamer 5'-TTGACA-3'. There is little or no effect on the activities of the wild-type and 23 other mutant ant promoters, including one with T.A at -33. The mutant sigma also activates E. coli lac promoters with A.T or C.G, but not T.A, at the corresponding position. The rpoD mutation (rpoD-RH588) changes a CGT codon to CAT. The corresponding change in sigma 70 is Arg588----His. This residue is in a region that is conserved among most sigma factors, a region that is also homologous with the helix-turn-helix motif of DNA-binding proteins. These results suggest that this region of sigma 70 is directly involved in recognition of the -35 hexamer.
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PMID:A mutant Escherichia coli sigma 70 subunit of RNA polymerase with altered promoter specificity. 266 27

Coliphage lambda gene expression is regulated temporally by systems of termination and antitermination of transcription. The lambda-encoded N protein (pN) acting with host factors (Nus) at sites (nut) located downstream from early promoters is the first of these systems to operate during phage development. We report observations on some of the components of this complex system that, in part, address the way in which these elements interact to render RNA polymerase termination-resistant. (1) The isolation of a conditionally lethal cold-sensitive nusA mutation demonstrates that NusA is essential for bacterial growth. (2) The effect on lambda growth in a host in which the Salmonella NusA protein is overproduced suggests that NusA is essential for N-mediated antitermination in phage lambda. (3) A truncated NusA product, representing only the amino two-thirds of the native protein, is active for both bacterial growth and pN action, indicating that the carboxy end of the molecule may not be a functionally important region. (4) lambda pN can function with the heterologous nut region from Salmonella typhimurium phage P22 when lambda pN is overproduced, demonstrating that lambda pN can function with the nut regions of other lambdoid phages. (5) A single base-pair change in the lambda nutR boxA sequence that was selected to permit a lambda derivative to utilize the Salmonella NusA protein restores lambda growth in the Escherichia coli nusA1 host.
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PMID:lambda N antitermination system: functional analysis of phage interactions with the host NusA protein. 282 Dec 65

Bacteriophage 434 encodes a repressor that, like bacteriophage lambda repressor, both activates and represses transcription. As in the lambda chromosome, a region of the 434 chromosome, called the right operator, contains three repressor binding sites (OR1, OR2, and OR3) that mediate these effects on two adjacent promoters. We now show that a part of the 434 repressor, the amino-terminal domain, activates leftward transcription when bound to OR2. We show that 434 repressor bound to OR2 closely approaches (touches) RNA polymerase bound to the leftward promoter. Model building based on ethylation interference and other experiments suggests that in three cases, those involving lambda repressor, 434 repressor, and bacteriophage P22 repressor, and in spite of differences in detailed arrangements, transcription is activated by a contact between the repressor and the same part of RNA polymerase.
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PMID:Activation of transcription by the bacteriophage 434 repressor. 346 10

Bacteriophage MB78 cannot grow on rifampicin resistant mutant of host Salmonella typhimurium (rif39) which contains an altered beta subunit of RNA polymerase. Bacteriophage P22, however, grows normally in rif39 both in the presence or absence of rifampicin. Perhaps MB78 promoter is not recognized by altered RNA polymerase. As the phage P22 helps MB78 to grow to some extent on rif39, hybrids between P22 and MB78 have been isolated. Hybrid phage which can grow on rif39 contains mostly genes from MB78 although a small portion (15-20 per cent) of the genome belongs to P22 genome which helps MB78 to overcome the transcription inhibition in the host mutant with altered RNA polymerase.
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PMID:Bacteriophage P22 helps bacteriophage MB78 to overcome the transcription inhibition in rifampicin resistant mutant of Salmonella typhimurium. 390 24

Mutants of Salmonella typhimurium defective in adenylate cyclase (cya gene) or in cAMP receptor protein (crp gene) are lysogenized at reduced frequency by phage P22. One class of the bacterial mutants with an altered RNA polymerase (rif gene) is also lysogenized at reduced frequency. In the three types of mutant bacteria, the phage's decision between lysogeny and lysis is shifted to lysis and the phage form clear plaques. We propose that in wild-type bacteria the cAMP-receptor protein, in combination with cAMP, activates bacterial RNA polymerase to transcribe certain phage genes that are required for efficient lysogenization. Under conditions of strong catabolite repression, when the supply of energy and biosynthetic components is abundant and the concentration of cAMP is low, the phage would multiply and lyse the cell. When the supply of energy is deficient and the concentration of cAMP is high, the phage would lysogenize the cell. Phage mutants have been isolated that form turbid plaques on the three classes of bacterial mutants due to a higher frequency of lysogeny. These phage mutants have been shown by complementation to be defective in the same gene, which we have called the cly gene. These cly mutants lysogenize the wild-type bacteria with a 99% frequency and, thus, do not form plaques on them. Other kinds of bacterial mutants are also lysogenized at reduced frequency by phage P22. They may be altered in other physiological control systems that influence the frequency of lysogenization.
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PMID:Adenosine 3':5'-cyclic monophosphate concentration in the bacterial host regulates the viral decision between lysogeny and lysis. 433 51

It has been suggested that the lambda repressor stimulates transcription of its own gene by binding to the lambda operator and contacting RNA polymerase bound to the adjacent promoter. We describe three different mutants (called pc) of the lambda phage repressor that are specifically deficient in the positive control function. We show that the amino acid residues altered in the pc mutants lie on the surface of the DNA-bound repressor that we predict, based on structural and other evidence, would most closely approach DNA-bound polymerase. Furthermore, we describe a pc mutant of the P22 repressor. We argue that in both the lambda and P22 repressors a structure comprised of two alpha helices has two functions: to bind DNA and to contact RNA polymerase. In the two cases, however, different regions of this structure contact polymerase to mediate positive control.
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PMID:Repressor structure and the mechanism of positive control. 621 86

Spontaneous mutants of Salmonella typhimurium isolated in our laboratory from thiolutin-containing tryptone agar plates are partially resistant to thiolutin in enriched media. In minimal media, they are not resistant. The mutants are not temperature sensitive but fail to support the development of phage P22 at higher temperatures (40 degrees C). Thiolutin did not interfere with RNA polymerase or nucleotide kinase in in vitro experiments. However, thiolutin did inhibit the rate of incorporation of exogenous uridine into the cellular pool and consequently the acid-precipitable material. It appears that one site of action of thiolutin is at the membrane level.
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PMID:Thiolutin-resistant mutants of Salmonella typhimurium. 675 84

Dimers of P22 Arc repressor bind to half-sites of the 21 bp arc operator and interact cooperatively to stabilize a DNA-bound tetramer. Mutation of Ser35 (a residue in the dimer-dimer interface) to Arg or Leu disrupts cooperative binding. The mutant proteins have near wild-type stabilities, give operator footprints like wild-type, and prevent binding of RNA polymerase to the Pant promoter in vitro. These mutants are, however, largely inactive in vivo. Thus, although cooperativity is not structurally required for repression, it appears that the additional DNA-binding energy from dimer-dimer cooperativity is required for normal biological function. Altering the spacing between the DNA half-sites by even one base-pair eliminates dimer-dimer cooperativity, indicating that Arc dimers need to be oriented correctly by half-site binding to allow the interactions that stabilize the tetrameric complex.
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PMID:P22 Arc repressor: role of cooperativity in repression and binding to operators with altered half-site spacing. 760 85

Lysogenic induction of bacteriophage lambda is controlled by the action of the phage repressor and Cro proteins at the phage right operator (O(R)). This study examines the roles of the repressor and Cro proteins of the related phage 434. The start sites of transcription of the divergently oriented promoters in the 434 O(R) region, PR and PRM, were mapped, and the effects of 434 repressor and Cro on promoter activity were assessed using promoter fusions to lacZ. The effects of repressor or Cro bound to each of the operator subsites (O(R)1, O(R)2 and O(R)3) were assessed by examining regulation in the presence of operator mutations. The binding of Cro to a 434 operator was probed by an ethylation interference experiment which, together with other data, indicates that 434 Cro and repressor probably turn off transcription by blocking binding of RNA polymerase to promoter sequences. In general, the 434 and lambda right operators are controlled in a similar fashion, but differences in detail were also encountered: (1) 434 Cro represses transcription from PR primarily by binding to O(R)1, whereas binding of lambda Cro to O(R)1 and O(R)2 contribute equally to repression. (2) The 434 cI message, unlike that of lambda, has a recognizable homology to the Shine-Dalgarno ribosome binding site. (3) Occupancy of O(R)3 by repressor may be somewhat greater in a 434 lysogen than in a lambda lysogen. (4) The 434 repressor probably activates transcription when bound at O(R)2 by contacting RNA polymerase, as does lambda repressor, but also by influencing competition between PR and PRM. An analysis of the six right operator systems for which data are available indicates that all six repressors may employ the mechanism of transcriptional activation first described for lambda, P22 and 434: apposition of an acidic surface to a particular part of RNA polymerase.
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PMID:The bacteriophage 434 right operator. Roles of O(R)1, O(R)2 and O(R)3. 845 May 41


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