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Query: EC:4.1.99.3 (PRE)
 1,923 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We used a simian virus 40-based shuttle vector plasmid, pZ189, to determine the role of pyrimidine cyclobutane dimers in UV light-induced mutagenesis in monkey cells. The vector DNA was UV irradiated and then introduced into monkey cells by transfection. After replication, vector DNA was recovered from the cells and tested for mutations in its supF suppressor tRNA marker gene by transformation of Escherichia coli carrying a nonsense mutation in the beta-galactosidase gene. When the irradiated vector was treated with E. coli photolyase prior to transfection, pyrimidine cyclobutane dimers were removed selectively. Removal of approximately 90% of the pyrimidine cyclobutane dimers increased the biological activity of the vector by 75% and reduced its mutation frequency by 80%. Sequence analysis of 72 mutants recovered indicated that there were significantly fewer tandem double-base changes and G X C----A X T transitions (particularly at CC sites) after photoreactivation of the DNA. UV-induced photoproducts remained (although at greatly reduced levels) at all pyr-pyr sites after photoreactivation, but there was a relative increase in photoproducts at CC and TC sites and a relative decrease at TT and CT sites, presumably due to a persistence of (6-4) photoproducts at some CC and TC sites. These observations are consistent with the fact that mutations were found after photoreactivation at many sites at which only cyclobutane dimers would be expected to occur. From these results we conclude that UV-induced pyrimidine cyclobutane dimers are mutagenic in DNA replicated in monkey cells.
Mol Cell Biol 1986 Oct
PMID:UV light-induced cyclobutane pyrimidine dimers are mutagenic in mammalian cells. 354 May 89

Irradiation of dominant marker DNA with UV light (150 to 1,000 J/m2) was found to stimulate the transformation of human cells by this marker from two- to more than fourfold. This phenomenon is also displayed by xeroderma pigmentosum cells (complementation groups A and F), which are deficient in the excision repair of UV-induced pyrimidine dimers in the DNA. Also, exposure to UV of the transfected (xeroderma pigmentosum) cells enhanced the transfection efficiency. Removal of the pyrimidine dimers from the DNA by photoreactivating enzyme before transfection completely abolished the stimulatory effect, indicating that dimer lesions are mainly responsible for the observed enhancement. A similar stimulation of the transformation efficiency is exerted by 2-acetoxy-2-acetylaminofluorene modification of the DNA. No stimulation was found after damaging vector DNA by treatment with DNase or gamma rays. These findings suggest that lesions which are targets for the excision repair pathway induce the increase in transformation frequency. The stimulation was found to be independent of sequence homology between the irradiated DNA and the host chromosomal DNA. Therefore, the increase of the transformation frequency is not caused by a mechanism inducing homologous recombination between these two DNAs. UV treatment of DNA before transfection did not have a significant effect on the amount of DNA integrated into the xeroderma pigmentosum genome.
Mol Cell Biol 1985 Apr
PMID:UV stimulation of DNA-mediated transformation of human cells. 399 Jun 93

The yeast Saccharomyces cerevisiae, like most organisms, is able to directly repair pyrimidine dimers by using a photoreactivating enzyme and visible light. Cells carrying the phr1 mutation were shown previously to be unable to photoreactivate dimers, but neither the map position nor the primary gene product of the PHR1 gene has been determined. We have cloned this gene and determined its map position. A plasmid containing a 6.4-kilobase yeast DNA insert has been isolated and shown to restore photoreactivation in a phr1 strain. A 3.1-kilobase subclone has also been shown to complement phr1. The original plasmid was targeted to integrate into chromosomal DNA at a site homologous to the insert by cutting within the insert. Two of these integrants have been mapped on the right arm of chromosome XV; the integrants have been further mapped at ca. 13 centimorgans from prt1. It has also been independently determined that phr1 maps at this location. Thus, we have determined the map position of PHR1 and also have shown that the plasmid contains PHR1 rather than a suppressor of the phr1 mutation.
Mol Cell Biol 1984 Sep
PMID:Cloning and mapping of Saccharomyces cerevisiae photoreactivation gene PHR1. 609 43

Abortive and productive initiation assays were used to study transcription initiation at the PRE promoter of phage lambda in vitro. Two parameters were measured: k2, the rate constant for the transition between closed and open complexes; and KB, the equilibrium constant for the initial binding of RNA polymerase to promoter DNA. In the absence of cII protein (which activates PRE) the PRE promoter was extremely weak as expected, with k2 = 4.0 X 10(-4) S-1 and KB = 1.0 X 10(7) M-1. The addition of cII protein resulted in about a 15-fold increase in KB and a 40-fold increase in k2. Thus, cII activation of PRE results both in enhanced binding of RNA polymerase to DNA to form closed complexes and in an enchanced rate of isomerization of closed to open complexes. In addition, we found that open complexes formed in the presence of cII protein were at least four times as stable as those formed in its absence. This suggests that RNA polymerase and cII protein may remain in close contact even after complexes are formed.
J Mol Biol 1984 Feb 05
PMID:Role of cII protein in stimulating transcription initiation at the lambda PRE promoter. Enhanced formation and stabilization of open complexes. 622 41

The efficiency of translation of the cII gene of bacteriophage lambda is greatly reduced by the cII3059 mutation, a GUU----GAU (Val----Asp) change in the second cII codon. Mutations in the third and fourth codons of the cII gene, called ctr mutations, reverse this translation deficiency. Lambda cII3059 ctr-1, which has a GCA----ACA (Ala----Thr) change in the fourth cII codon, produces about half the normal level of cII activity in liquid cultures, and lambda cII3059 ctr-2 and lambda cII3059 ctr-3, which have identical CGT----CGC changes in the third codon, produce normal levels of cII activity in liquid culture. Since the cII protein of ctr-3 has the same primary sequence as that of lambda cII3059, the cII- phenotype of lambda cII3059 can be explained entirely by the deficiency of translating cII mRNA. We propose that ctr mutations increase translation efficiency by destabilizing a stable stem structure which can be formed by cII mRNA. The ctr mutations lie in an overlapping regulatory region which contains, in addition to sequence elements that influence the rate of cII translation, a region to which cII protein binds to activate transcription from the PRE promoter. The ctr-1 mutation alters the cII recognition sequence from 5'-T-T-G-C-N6T-T-G-C-3' to 5'-T-T-G-C-N6T-T-G-T-3', but has no effect on PRE activity. Since a C----T change in the first (5'-proximal) T-T-G-C sequence (to yield 5'-T-T-G-T-N6T-T-G-C) greatly lowers cII binding affinity, cII protein must not recognize the two T-T-G-C sequences in an identical manner.
J Mol Biol 1984 Dec 25
PMID:Mutations that alter the DNA binding site for the bacteriophage lambda cII protein and affect the translation efficiency of the cII gene. 624 Dec 64

In order to study the structural organization and regulation of the expression of the nitrogenase gene cluster in Rhizobium leguminosarum PRE we selected relevant subfragments of the sym-plasmid from clone banks by homology with R. meliloti nif-genes. Site-directed Tn5 mutagenesis was applied to a nif DH-specific clone and subsequently the transposon insertions were transferred back into the wild-type rhizobial genome by homologous recombination. Phenotypic effects of Tn5 mutations in the region of the structural nif-genes were determined by measuring acetylene reduction in nodulated plants and by immunological analysis of bacteroid-specific proteins. The localization of Tn5 insertion sites was in accordance with observed consequences: two genotypically different Tn5-induced mutations within nif D caused repression of CI alpha and beta synthesis and a strong reduction of CII production, thus resulting in a Fix- phenotype. Expression of different cloned Rhizobium DNA inserts, bearing nif K, nif D, nif H, or nif DH, was achieved in Escherichia coli minicells dependent upon the presence of a strong upstream vector promoter sequence. Gene products were identified by immunoprecipitation with specific antisera. Endogenous rhizobial transcriptional start signals in one case (nif H) seemed to be recognized at a low rate by the E. coli system; in contrast, Rhizobium ribosome binding sites for all three structural nif-genes functioned normally in minicells. The approximate location of the coding regions for nif KDH genes was determined and found to be contiguous.
J Mol Appl Genet 1984
PMID:Molecular cloning and functional characterization of Rhizobium leguminosarum structural nif-genes by site-directed transposon mutagenesis and expression in Escherichia coli minicells. 633 Feb 64

An Escherichia coli recA phr+ purA strain was more resistant to ultraviolet radiation than its isogenic derivative recA phr+ purA+ in the absence of photoreactivating light, whereas their nearly isogenic derivative recA phr showed most UV-induced lethality. The amounts of photoreactivating enzyme (PRE) per cell in the recA phr+ purA was higher than in the recA phr+ purA+. The recA phr is defective for photoreactivation. Thus, in the recA strain, UV resistance in the dark increased in proportion to the amounts of PRE per cell, suggesting that PRE participates in the process of dark repair of UV-damaged DNA.
Mol Gen Genet 1983
PMID:Evidence that the phr+ gene enhances the ultraviolet resistance of Escherichia coli recA strains in the dark. 635 98

Escherichia coli DNA photolyase (photoreactivating enzyme) was purified to homogeneity from a strain that greatly overproduces the protein. The purified enzyme has absorption peaks at 280 and 380 nm, a fluorescence emission peak at 480 nm and, upon denaturation, releases a chromophore that has the spectroscopic properties of flavin adenine dinucleotide (FAD), indicating that FAD is an intrinsic chromophore of the enzyme.
J Mol Biol 1984 Jan 15
PMID:Escherichia coli DNA photolyase is a flavoprotein. 636 15

Fibroblasts from Xenopus laevis, which possess photoreactivating enzyme were used to study the influence of photoreactivating light on the frequency of pyrimidine dimers in DNA, chromosomal aberrations, sister chromatid exchanges, cell killing and the induction of gene mutations (ouabain-resistance) induced by 254 nm ultraviolet irradiation. The frequency of all biological endpoints studied were reduced following exposure to photoreactivating light parallel to the reduction in the frequencies of pyrimidine dimers (determined as endonuclease sensitive sites). However there was not always an absolute quantitative relationship between the reduction in the frequency of pyrimidine dimers and the reduction in the biological effects. This probably reflects a fast fixation process for the biological effects prior to removal of the dimers by photoreactivation.
Mol Gen Genet 1980
PMID:Photoreactivation of UV induced cell killing, chromosome aberrations, sister chromatid exchanges, mutations and pyrimidine dimers in Xenopus laevis fibroblasts. 693 98

Phage P22 defective in gene 24 and harbouring the Oc mutation k5 in OR exhibits a strongly increased c2-repressor synthesis after infection of non-lysogenic S. typhimurium. The repressor synthesis depends strictly on an intact c1 gene. The kinetics of its synthesis, as monitored by polyacrylamide gel electrophoresis, is the same as with P22 c+, namely a turn off 8-10 min after infection. - After infection of P22-lysogenic bacteria with either P22 24- k5 or P22 24- k5 c1, much lower amounts of repressor are synthesized but again with the same kinetics. These results suggest a cro-like function acting at PRE and PRM of P22. The possible reason for the c2 overproduction is discussed.
Mol Gen Genet 1981
PMID:Kinetics of c2-repressor synthesis in a regulatory defective P22 mutant. 703 85


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