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

The influence of vitamin D nutrition on melanogenesis in skin induced by UV radiation was studied in pigmented adult rats. Melanogenesis, assessed by the activity of skin tyrosinase (radiometric assay), was studied in vitamin-D-deficient and vitamin-D-fed rats exposed to UV (0.1 J/cm2, 290-320 nm). The tyrosinase activity in skin was not significantly changed by vitamin D treatment alone. In contrast, the induction of tyrosinase activity provoked by UV radiation was greater in vitamin-D-fed than in vitamin-D-deficient rats. The increase in skin tyrosinase activity in response to UV was preceded by an increase in skin cAMP levels. This rise in cAMP was greater in vitamin-D-treated rats than in vitamin-D-deficient rats. The pretreatment of rats with phosphodiesterase inhibitor potentiated the effect of vitamin D on skin tyrosinase activity. The low serum calcium levels in the vitamin-D-deficient group were evidently not responsible for the lower UV induction of skin tyrosinase activity because the vitamin-D-deficient rats with normal serum calcium levels (supplemented with 20% lactose and 2% calcium in the diet) were also unable to show maximal induction of skin tyrosinase activity in response to UV radiation requires the presence of adequate vitamin D. cAMP may be involved in the mediation of this effect. The relationship observed between the vitamin D status of animals and tyrosinase activity of skin could provide an effective feed-back control for protection against UV and vitamin D intoxication.
Mol Cell Endocrinol 1982 Mar
PMID:Vitamin D nutrition increases skin tyrosinase response to exposure to ultraviolet radiation. 617 46

Mammary glands from parous mice required lower concentrations of hormones in vitro than those from virgins to effect differentiation, as measured by lactose synthetase activity. This phenomenon could not be explained by changes in receptor levels, since both mammary gland insulin and prolactin binding, although elevated at midpregnancy, returned to baseline in tissue from parous mice. Ethidium bromide, an intercalating dye, was a potent inhibitor of lactose synthetase induction in explants from virgins but much less potent in tissue from pregnant mice; explants from parous animals displayed intermediate sensitivity, suggesting that DNA structure was permanently altered. However, casein synthesis in glands from parous mice required hormone concentrations as high as in virgins and are just as susceptible to ethidium bromide as in virgins. Similarly, the vulnerability of the casein gene to DNAase I digestion is low in mammary epithelial cells from virgins, high in cells from pregnant mice, and low again in cells from parous animals. These data suggest that during the first pregnancy of mice, there are changes in the chromatin configuration that may facilitate the transcription of milk-related mRNA. Furthermore, after mammary gland involution these changes in the casein gene undergo reversion, while those involved with lactose synthetase activity persist; this may explain the disparate hormonal responsiveness seen in these animals with respect to casein and lactose synthesis.
Mol Cell Endocrinol 1984 May
PMID:Enhanced hormonal responsiveness in mammary glands from parous mice: molecular mechanisms. 620 88

A methodology for the analysis of the fine specificity of monoclonal anti-lactose IgM and IgG antibodies is described using structural variants of the homologous lactoside epitope. These variants are used as inhibitors of the binding of a reference ligand N-(5-dimethylaminonaphthalene-1-sulfonyl)-p-aminophenyl-beta-lactoside. Excitation of the antibody with bound ligand at 295 nm leads to resonance energy transfer to and fluorescence emission by the ligand. Titration of the antibody-ligand mixture with the inhibitor and measurement of the emission at 550 nm provide the data for the calculation of the binding constants of the inhibitors. A comparison of two IgM and two IgG antibodies showed that the higher affinity of the IgG antibodies arises from their specific interaction with both hexosides of the lactoside in contrast to IgM antibodies which do not engage the non-terminal hexoside as effectively. The quantitative significance of this difference is a differential free energy contribution of about -3 kcal/mole to the binding of lactoside by IgG. A finer discrimination between homologous and several cross-reactive molecules is evident with IgG antibody compared to IgM. The former exhibits about 100-fold greater difference in their binding constants than does IgM. These differences applied to biologically relevant multivalent interactions, where functional affinity governs complex formation, suggest a possible explanation for the IgM to IgG conversion characteristic of the humoral immune response.
Mol Immunol 1984 Oct
PMID:Restriction in IgM expression--V. Fine structure analysis in the anti-lactose system. 620 62

Garrett et al. (Mol. Gen. Genet. 182:326-331, 1981) constructed strains of Escherichia coli harboring derivatives of plasmid pBR322 that carry the lysis genes (S, R, and Rz) of phage lambda. The plasmid construction placed the genes under control of the lactose operon operator-promotor (and thus of lac repressor). Induction of E. coli strains carrying these plasmids resulted in rapid lysis of the culture unless the S gene was defective, in which case the cells grew normally. A freeze-thaw treatment of induced cells carrying an S- plasmid gave quantitative lysis of either E. coli or Salmonella typhimurium cells under exceptionally gentle conditions. The method was equally effective on exponential phase cells and stationary phase cells and was readily extended to a large number of independent cultures.
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PMID:Facile and gentle method for quantitative lysis of Escherichia coli and Salmonella typhimurium. 623 60

Casadaban (1976) developed a technique for isolating E. coli clones containing fusions of the amino terminal-encoding portion of any cistron with the carboxy terminal-encoding portion of lacZ. The technique utilizes prophage Mu homology to bring the two cistrons into proximity. I have followed the appearance over time of colonies containing araB-lacZ fusions from a strain where the beginning of the araB cistron is connected to lacZ by an intact Mucts62 prophage. Cultures of the starting strain grown on a variety of media have fewer than 2 in 10(10) cells capable of forming colonies within three days after plating on selective arabinose-lactose medium. At 32 degrees C, there is a delay of between 4 and 19 days before the first colony appears. The kinetics of colony appearance over the next two to four weeks then shows a rapid increase in the number of new colonies emerging per day followed by a decline. The pattern of colonial emergence and the final numbers of fusion colonies obtained are not grossly affected by reducing the number of cells plated over five orders of magnitude. Fusion colonies sometimes show a clustered pattern when they first emerge. Inoculation of pre-existing fusion clones at specific locations on the arabinose-lactose selection plates seeded with the starting strain leads to the formation of inhibitory zones where no fusion colonies appear. Selection plates contain many microcolonies and papillae which do not proliferate into scoreable colonies but nonetheless contain cells capable of growth when replated on the same selective medium. Up to 39% of all plated cells are capable of producing fusion clones. The kinetics of fusion colony appearance can be altered by environmental and genetic manipulations. Partial derepression of the Mucts prophage at 37 degrees accelerates the appearance of colonies but also reduces the final yield. Addition of limiting concentrations of glucose to the selective medium also accelerates the appearance of colonies in a specific fashion: enrichments below the level required for maximum acceleration produce a biphasic kinetics with two waves of fusion clone emergence separated by an eight-day interval. Infection with Muc+pAp phage produces dilysogens that have almost completely lost the ability to produce fusions. Infection with MuctsAampAp phage produces strains that are reduced in phage production and have delayed kinetics of fusion clone emergence. The implications of these observations for theories of hereditary change in bacteria are discussed.
Mol Gen Genet 1984
PMID:Observations on the formation of clones containing araB-lacZ cistron fusions. 623 72

The previously described hybrid plasmid pC7 which carries lacI+O+delta(Z)Y+A+ on a 12.3 X 10(6)-Mr DNA fragment [Teather et al. (1978) Mol. Gen. Genet. 159, 239-248] was partially digested with the restriction endonuclease EcoRI under conditions reducing the recognition sequence to d(A-A-T-T) and ligated to the vector pB322. lac Y-carrying inserts of various sized (Mr 1.5-4.7 X 10(6)) were obtained. Hybrid plasmid pTE18 (2300-base-pair insert) carries part of the I (repressor) gene, the promotor-operator region, part of the Z (beta-galactosidase) gene, the Y (lactose carrier) gene and part of the A (transacetylase) gene. Upon induction of pTE18-harbouring strains the Y-gene product is expressed at a nearly constant rate for several generations and accumulates to a level of 12-16% of the total cytoplasmic membrane protein. Integration into the membrane leads to active carrier as judged by binding and transport measurements.
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PMID:Lactose carrier protein of Escherichia coli. Structure and expression of plasmids carrying the Y gene of the lac operon. 625 Aug 28

We attempted to correlate structural modifications of the adenosine 3',5' cyclic monophosphate (cAMP) receptor protein (CAP), to changes in some of its in vivo regulatory functions such as (i) stimulation of the lactose operon expression and (ii) control of adenylate cyclase activity. A radioimmunological procedure was used to study the structure of CAP synthesized by three mutants (crpX) grown under various conditions, in the presence or absence of endogenous or exogenous cAMP. In one mutant CAP appears to be sensitive to thermal inactivation. In another mutant CAP is particularly sensitive to degradation in the absence of cAMP; this degradation is enhanced by high temperature and during stationary phase of growth, and prevented by the addition of glucose. Functional alterations of CAP were not found to follow structural changes strictly. In the crpX mutants and in strains carrying the crp+ or other crp allele, the stimulation of the lactose operon expression and the modulation of the in vivo rates of cAMP synthesis appear to vary in parallel, favoring an indirect mechanism of regulation of adenylate cyclase by CAP.
Mol Gen Genet 1982
PMID:crpX mutants of Escherichia coli K12: specific regulatory effects of altered cyclic AMP receptor proteins. 629 64

From fluorescence measurements we could analyse the binding of cyclic adenosine 3',5'-monophosphate receptor protein (CRP) from Escherichia coli to its specific site on a 301 base-pair long DNA fragment containing the control region of the lactose operon. At physiological ionic strength selection of the specific site is strictly dependent on the allosteric effector cAMP, and binding of the cAMP . CRP complex to its specific site is favoured over the non-specific binding by 5 kcal/mol with Kass (specific) = 10(8) M-1 at 37 degrees C.
J Mol Biol 1983 Jul 15
PMID:On the origin of selectivity in recognition by cyclic adenosine 3',5'-monophosphate receptor protein of its specific binding site of the lactose promoter region. 630 68

None of the Agrobacterium tumefaciens and A. rubi strains tested produces detectable amounts of beta-galactosidase although they are capable of utilizing lactose as sole source of carbon. This opportunity was taken to investigate the expression of lac transposon Tn951 (Cornelis et al. 1978) in Agrobacterium with the ultimate goal of using this system to investigate alien gene expression. When the transposon was introduced with the help of a broad-host range plasmid, RP1, the transconjugants produced significant quantities of beta-galactosidase which was inducible by isopropyl-beta-D-thiogalactopyranoside. Tn951 was capable of restoring the Lac+ phenotype to an A. tumefaciens mutant not capable of using lactose. Cellobiose, a known inducer of aldohexopyranoside: cytochrome c oxidoreductase (which regulates the characteristic 3-ketolactose production in Agrobacterium; van Beeumen and De Ley (1968), had no effect on beta-galactosidase activity.
Mol Gen Genet 1984
PMID:Studies on Tn951 (lac+) expression in Agrobacterium. 632 25

The DNA sequence spanning coordinates 9.9 to 16.4 kilobases of the lactose transposon Tn951 ( Cornelis et al., Mol. Gen. Genet. 160:215-224, 1978) constitutes a transposable element by itself. Unlike Tn951 ( Cornelis et al., Mol. Gen. Genet. 184:241-248, 1981), this element, called Tn2501 , transposes in the absence of any other transposon. Transposition of Tn2501 proceeds through transient cointegration and duplicates 5 base pairs of host DNA. Tn2501 is flanked by nearly perfect inverted repeats (44 of 48), related to the inverted repeats of Tn21 ( Zheng et al., Nucleic Acids Res. 9:6265-6278, 1982). Unlike Tn21 , Tn2501 does not confer mercury resistance.
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PMID:Detection and characterization of Tn2501, a transposon included within the lactose transposon Tn951. 632 43


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