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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

One allele at each of the five nit loci in Neurospora crassa together with the wild type strain have been compared on various nitrogen sources with regard to (i) their growth characteristics (ii) the level of nitrate reductase and its associated activities (reduced benzyl viologen nitrate reductase and cytochrome c reductase) (iii) the level of nitrate reductase and (iv) their ability to take up nitrite from the surrounding medium. Results are consistent with the hypothesis that nit-3 is the structural gene for nitrate reductase, nit-1 specifies in part of molybdenum containing moiety which is responsible for the nit-3 gene product dimerising to form nitrate reductase, nit-4 and nit-5 are regulator genes whose products are involved in the induction of both nitrate reductase and nitrite reductase and nit-2 codes for a generalised ammonium activated repressor protein. Studies on the induction of nitrate reductase (and its associated activities) and nitrite reductase in wild type, nit-1 and nit-3 in the presence of either nitrate or nitrite suggest that each enzyme may be regulated independently of the other and that nitrite could be true co-inducer of the assimilatory pathway. Nitrite uptake experiments with nit-2, nit-4 and nit-5 strains show that whereas nit-4 and nit-5 are freely permeable to this molecule, it is unable to enter the nit-2 mycelium.
Mol Gen Genet 1976 May 07
PMID:Biochemical studies on the nit mutants of Neurospora crassa. 13 3

The synthesis and regulation of two of the enzymes of the biotin operon of Escherichia coli, 7,8-diaminopelargonic acid aminotransferase and dethiobiotin synthetase, were studied in vitro in a coupled transcription-translation system. These enzymes are encoded by genes located on opposite strands of the divergently transcribed operon (A. Guha, Y. Saturen, and W. Szybalski, J. Mol. Biol. 56:53-62, 1971). The kinetics of synthesis of both the enzymes were determined and the efficiency of the system was 0.3 to 0.4% that of the in vivo rate of synthesis in derepressed cells. Guanosine 3'-diphosphate 5'-diphosphate at 0.2 mM concentration stimulated the synthesis of 7,8-diaminopelargonic acid aminotransferase two- to threefold but had no effect on dethiobiotin synthetase synthesis. Biotin, which was most effective as the corepressor in vivo, also functioned in vitro at physiological concentrations in conjunction with a crude repressor protein isolated from a lysogen carrying the bioR gene. However, the two strands showed differential repression. At a repressor concentration where 7,8-diaminopelargonic acid aminotransferase synthesis was completely repressed, the repression of dethiobiotin synthetase was only 20% and did not exceed 50% with increasing repressor concentrations. Although the exact reason for the partial repression remains to be resolved, our data clearly suggest that the biotin operon is regulated from two separate operators.
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PMID:In vitro synthesis and and regulation of the biotin enzymes of Escherichia coli K-12. 35 Aug 35

Understanding the mechanism of glucose repression in yeast has proved to be a difficult and challenging problem. A multitude of genes in different pathways are repressed by glucose at the level of transcription. The SUC2 gene, which encodes invertase, is an excellent reporter gene for glucose repression, since its expression is controlled exclusively by this pathway. Genetic analysis has identified numerous regulatory mutations which can either prevent derepression of SUC2 or render its expression insensitive to glucose repression. These mutations allow us to sketch the outlines of a pathway for general glucose repression, which has several key elements: hexokinase PII, encoded by HXK2, which seems to play a role in the sensing of glucose levels; the protein kinase encoded by SNF1, whose activity is required for derepression of many glucose-repressible genes; and the MIG1 repressor protein, which binds to the upstream regions of SUC2 and other glucose-repressible genes. Repression by MIG1 requires the activity of the CYC8 and TUP1 proteins. Glucose repression of other sets of genes seems to be controlled by the general glucose repression pathway acting in concert with other mechanisms. In the cases of the GAL genes and possibly CYC1, regulation is mediated by a cascade in which the general pathway represses expression of a positive transcriptional activator.
Mol Microbiol 1992 Jan
PMID:Glucose repression in the yeast Saccharomyces cerevisiae. 131 Jul 93

We have studied the effect of the Tn10-encoded Tet repressor on expression from 13 cauliflower mosaic virus (CaMV) 35S promoter derivatives that contain a tet operator sequence in various positions downstream of the TATAbox. When the operator sequence was inserted less than 33 bp away from the TATAbox (position +9 with respect to the transcription start site), the repressor interfered with transcription, whereas increasing the distance to 35 bp (position +11) abolished repression. This result indicates that initiation of transcription from the CaMV 35S promoter occurs in at least two different steps: (1) binding of transcription factors, involving sequences extending to position +9; this step can be inhibited by binding of the Tet repressor protein; and (2) initiation of transcription from this complex, which is not affected by the repressor protein. We suggest that the Tet repressor can be used to investigate whether transcription conditions in vitro truly reflect the in vivo situation.
Mol Gen Genet 1992 Mar
PMID:The Tn10-encoded Tet repressor blocks early but not late steps of assembly of the RNA polymerase II initiation complex in vivo. 131 38

Initiation of transcription from the cytRP promoter in Escherichia coli is activated by the cAMP-CRP complex and negatively regulated by the CytR repressor protein. By combining gel retardation and footprinting assays, we show that cAMP-CRP binds to a single site centered at position -64 and induces a considerable bend in the DNA. CytR binds to a region immediately downstream from, and partially overlapping, the CRP site, and induces a modest bend into the DNA. In combination, cAMP-CRP and CytR bind co-operatively to cytRP forming a nucleoprotein complex in which the proteins directly interact with each other and bind to the same face of the DNA helix. CytR binding concomitantly antagonizes the cAMP-CRP-induced bend. This study indicates that the minimal DNA region required to obtain CytR regulation consists of a single binding site for each of cAMP-CRP and CytR. The case described here, in which a protein-induced DNA bend is modulated by a second protein, may illustrate a mechanism that applies to other regulatory systems.
J Mol Biol 1992 Sep 20
PMID:cAMP-CRP activator complex and the CytR repressor protein bind co-operatively to the cytRP promoter in Escherichia coli and CytR antagonizes the cAMP-CRP-induced DNA bend. 132 49

Expression of the Cob operon in Salmonella typhimurium is repressed by cobalamin (Cbl). Here it is shown that Cbl repression is mediated by a post-transcriptional regulatory mechanism that requires sequences within the leader and the first translated open reading frame, the cbiA gene. Transcriptional and translational Cob::lacZ fusions containing various lengths of Cob DNA were analysed. In a translational Cob::lacZ fusion 407 bp of leader sequence (+69 to +476) was sufficient to confer normal repression. However in a transcriptional Cob::lacZ fusion a 618 bp region (+69 to +687) was required for normal repression. This 618 bp region included sequences in the leader as well as sequences within the cbiA gene. Point mutations which resulted in loss of repression control were isolated and shown to be clustered in the leader sequence (+257 to +380). This region contains a putative hairpin-loop structure which we propose functions as an RNA operator site for a vitamin B12-responsive repressor protein.
Mol Microbiol 1992 Mar
PMID:Cobalamin (vitamin B12) repression of the Cob operon in Salmonella typhimurium requires sequences within the leader and the first translated open reading frame. 137 46

When theoretical methods are used to predict the properties of a given system, such as the effects of the substitution of a specific amino acid on the activity or stability of a protein as a whole, the accuracy of the prediction is directly dependent on the validity of the underlying model. A common error, however, is to attempt to improve a basically crude model by performing one aspect of the calculation in a rigorous manner. The accuracy of the model as a whole will remain limited by the crudest approximation or weakest assumption. To demonstrate the principle that nothing can be gained by performing extensive calculations using a basically crude underlying model we compare the predictive power of three models in relation to activity and stability data for 78 triple-site sequence variants of the lambda-repressor protein. This system has recently been analysed in terms of a conceptionally simple, but computationally elaborate model for the prediction of the energy of a protein in which amino acid residues in the core of the protein have been mutated. We show that comparable, if not better agreement with the experimental data can be reached using either of two much simpler models, based on straightforward structural considerations, which do not require elaborate calculations on a computer.
J Mol Biol 1992 Sep 20
PMID:Prediction of the activity and stability effects of site-directed mutagenesis on a protein core. 140 60

Induction of the lactose-galactose regulon is strongly repressed by glucose in some but not all strains of Kluyveromyces lactis. We show here that in strongly repressed strains, two to three times less Kl-GAL4 mRNA is synthesized and that expression of structural genes in the regulon such as LAC4, the structural gene for beta-galactosidase, is down regulated 40-fold or more. Comparative analysis of strains having a strong or weak repression phenotype revealed a two-base difference in the promoter of the Kl-GAL4 (also called LAC9) positive regulatory gene. This two-base difference is responsible for the strong versus the weak repression phenotype. The two base changes are symmetrically located in a DNA sequence having partial twofold rotational symmetry (14 of 21 bases). We hypothesize that this region functions as a sensitive regulatory switch, an upstream repressor sequence (URS). According to our model, the presence of glucose in the culture medium signals, by an unidentified pathway, a repressor protein to bind the URS. Binding reduces transcription of the Kl-GAL4 gene so that the concentration of the Kl-GAL4 protein falls below the level needed for induction of LAC4 and other genes in the regulon. For strains showing weak glucose repression, we hypothesize that the two base changes in the URS reduce repressor binding so that the regulon is not repressed. Our results illustrate an important principle of genetic regulation: a small (2- to 3-fold) change in the concentration of a regulatory protein can produce a large (40-fold or greater) change in expression of structural genes. This mechanism of signal amplification could play a role in many biological phenomena that require regulated transcription.
Mol Cell Biol 1992 May
PMID:The signal for glucose repression of the lactose-galactose regulon is amplified through subtle modulation of transcription of the Kluyveromyces lactis Kl-GAL4 activator gene. 156 29

A crude protein extract of Bacillus subtilis W23 contains a sequence-specific DNA binding activity for the xyl operator as detected by the gel mobility shift assay. A xylR determinant encoded on a multicopy plasmid leads to increased expression of this binding activity. In situ footprinting analysis of the protein-DNA complex in a polyacrylamide gel shows that the xyl operator is sequence-specifically bound and protected from cleavage by copper-phenanthroline at 26 phosphodiester bonds on each strand. Quantitative competition assays for repressor binding reveal that a 25 bp synthetic xyl operator cloned into a polylinker is bound with the same affinity as the operator in the wild-type xyl regulatory region. This confirms that no additional sites in the wild-type sequence contribute to repressor binding. The xyl operator consists of ten palindromic base pairs flanking five central non-palindromic base pairs. A mutational analysis shows that the sequence of the central base pairs contributes to recognition by the repressor protein and that the spacing of the palindromic elements is crucial for repressor binding. An operator half site is not bound by the repressor. In vivo and in vitro induction studies suggest that, of several structurally similar sugars, xylose is the only molecular inducer of the Xyl repressor.
Mol Gen Genet 1992 Apr
PMID:Regulation of the Bacillus subtilis W23 xylose utilization operon: interaction of the Xyl repressor with the xyl operator and the inducer xylose. 158 10

The genes coding for the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter strain AR50 were cloned and partially sequenced. A novel lac operon was identified which contains genes coding for a lactose-binding protein (lacE), two integral membrane proteins (lacF and lacG), an ATP-binding protein (lacK) and beta-galactosidase (lacZ). The operon is transcribed in the order lacEFGZK. The operon is controlled by an upstream regulatory region containing putative -35 and -10 promoter sites, an operator site, a CRP-binding site probably mediating catabolite repression by glucose and galactose, and a regulatory gene (lacl) encoding a repressor protein which mediates induction by lactose and other galactosides in wild-type A. radiobacter (but not in strain AR50, thus allowing constitutive expression of the lac operon). The derived amino acid sequences of the gene products indicate marked similarities with other binding-protein-dependent transport systems in bacteria.
Mol Microbiol 1992 Jul
PMID:Molecular analysis of the lac operon encoding the binding-protein-dependent lactose transport system and beta-galactosidase in Agrobacterium radiobacter. 163 Mar 15


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