Disease relevance of PHR1

• However, despite the functional and structural similarities between yeast photolyase and the E. coli enzyme and complementation of the photoreactivation deficiency of E. coli phr mutants by PHR1, yeast photolyase failed to enhance excision repair in the bacterium [1].
• Effects of microinjected photoreactivating enzyme on thymine dimer removal and DNA repair synthesis in normal human and xeroderma pigmentosum fibroblasts [2].
• Cloning, sequencing, expression and characterization of DNA photolyase from Salmonella typhimurium [3].
• Yeast photoreactivating enzyme (PRE), preilluminated with wavelengths ranging from the near-UV to the red spectral region, forms with 254 nm-irradiated transforming DNA of Haemophilus influenzae enzyme-substrate complexes that are more efficiently photorepaired than complexes formed from non-preilluminated PRE [4].

High impact information on PHR1

• Photoreactivating enzyme (DNA photolyase; deoxyribocyclobutadipyrimidine pyrimidine-lyase, EC 4.1.99.3) repairs UV damage to DNA by utilizing the energy of near-UV/visible light to split pyrimidine dimers into monomers [5].
• A damage-responsive DNA binding protein regulates transcription of the yeast DNA repair gene PHR1 [6].
• Transcription of PHR1 increases in response to treatment of cells with 254-nm radiation and chemical agents that damage DNA [6].
• Copper-phenanthroline footprinting of PRP-DNA complexes revealed that PRP protects a 39-base-pair region of PHR1 5' flanking sequence beginning 40 base pairs upstream from the coding sequence [6].
• In this communication, we report the identification of two proteins, Rph1p and Gis1p, that regulate PHR1 expression through URS(PHR1) [7].

Biological context of PHR1

• Basal-level and damage-induced expression of PHR1 require an upstream activation sequence, UAS(PHR1), which has homology with DRC elements found upstream of at least 19 other DNA repair and DNA metabolism genes in yeast [8].
• The primary regulator of the PHR1 damage response is a 39-bp sequence called URS(PHR1) which is the binding site for a protein(s) that constitutes the damage-responsive repressor PRP [7].
• Both proteins contain two putative zinc fingers that are identical throughout the DNA binding region, and deletion of both RPH1 and GIS1 is required to fully derepress PHR1 in the absence of damage [7].
• Rph1, a Cys2-His2 zinc finger protein, binds to an upstream repressing sequence of the photolyase gene PHR1, and represses its transcription in response to DNA damage in Saccharomyces cerevisiae [9].
• Phosphorylation of Rph1, a damage-responsive repressor of PHR1 in Saccharomyces cerevisiae, is dependent upon Rad53 kinase [9].

Anatomical context of PHR1

• Characterization of Pneumocystis carinii PHR1, a pH-regulated gene important for cell wall Integrity [10].
• The phr1 expression was also detected in presence of alpha-tomatine, a glycoalkaloid from tomato damaging cell membranes, suggesting that phr1 is induced by this cellular stress [11].
• The opposite was true also as HeLa cell free extract specifically inhibited the photorepair of a thymine dimer by DNA photolyase and its removal by (A)BC excinuclease [12].

Associations of PHR1 with chemical compounds

• The Saccharomyces cerevisiae DNA repair gene PHR1 encodes a photolyase that catalyzes the light-dependent repair of pyrimidine dimers [7].
• Using a PHR1-lacZ fusion gene in which expression of beta-galactosidase is regulated by PHR1 5' regulatory elements, we found that exposure of cells to 254-nm light, 4-nitroquinoline-N-oxide, methyl methanesulfonate, and N-methyl-N'-nitro-N-nitrosoguanidine induced synthesis of increased amounts of fusion protein [13].
• PHR1-related proteins have been implicated in glucan cell wall stability under various environmental conditions [10].
• Epdlp could be involved in cell wall maintenance and is essential for pseudohyphal growth induced by CEN and n-hexadecane at pH 4 and by n-hexadecane at pH 7.) In this paper, we cloned EPD2 of C. maltosa, which is highly similar to EPD1, PHR1, and PHR2 [14].
• Yeast DNA photolyase, purified by affinity chromatography, ran as a single component when analyzed by either electrophoresis on polyacrylamide gradient gels or by sedimentation velocity through 5-20% sucrose gradients containing 0.4 M KCl, and, therefore, was considered homogeneous [15].

Regulatory relationships of PHR1

• Multiple copies of UME6 stimulate expression from UAS(PHR1) and the intact PHR1 gene [8].

Other interactions of PHR1

• Deletion of UME6 abolishes this induction, decreases the steady-state concentration of photolyase molecules and PHR1 mRNA, and increases the UV sensitivity of a rad2 mutant [8].
• A C. glabrata gene family, CgGAS1-3, that shares significant homologies with both the GAS1 gene of Saccharomyces cerevisiae, which is necessary for cell wall assembly, and the pH-regulated genes PHR1 and PHR2 of Candida albicans, which are involved in cell wall assembly and required for virulence, has been cloned [16].
• We showed that PHR1 immunoprecipitates with either myosin tail by using protein extracts from cotransfected HEK293 cells [17].
• The process by which Pneumocystis carinii constructs its cell wall is not well known, although recent studies reveal that molecules such as beta-1-3-glucan synthetase (GSC1) and environmental pH-responsive genes such as PHR1 are important for cell-wall integrity [18].
• Under inducing conditions, E. coli cells carrying the tac-PHR1 plasmid pCB1241 accumulate up to 8% of total cellular protein as yeast photolyase; similarly, the GAL10-PHR1 fusion plasmid pGBS107 directs the synthesis of at least 1800-2400 molecules of photolyase per log-phase yeast cell [19].

Analytical, diagnostic and therapeutic context of PHR1

• We have utilized chemical modification and site-directed mutagenesis to probe the interactions involved in substrate recognition by the yeast photolyase Phr1 [20].
• Unscheduled DNA synthesis in xeroderma pigmentosum cells after microinjection of yeast photoreactivating enzyme [21].
• The activity of purified DNA photolyase from Baker's yeast is enhanced by a compound (Activator (III)) obtained from yeast by chloroform extraction ion exchange chromatography and gel filtration [22].

References