Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

This paper reports the characterization of novel mutations within the Arabidopsis thaliana HY4 gene, which has previously been shown to encode a protein (CRY1) with characteristics of a blue-light photoreceptor. Several point mutations were identified within the amino-terminal domain of CRY1--this region of CRY1 has high homology to photolyase and is likely to be involved in blue-light-mediated electron transfer. Mutations were found within the region of homology to the known chromophore binding domains of photolyase. Point mutations within the 200 amino acid carboxy-terminal extension distinguishing CRY1 from photolyase, likewise disrupt function of the protein. CRY1 was originally defined as the photoreceptor responsible for blue-light-mediated inhibition of hypocotyl elongation and we now report that anthocyanin accumulation in germinating seedlings is an additional phenotype under the control of this photoreceptor--this is shown to be mediated in part by modulation of mRNA levels of chalcone synthase, one of the anthocyanin biosynthetic enzymes. The effect of the novel mutations on both inhibition of hypocotyl elongation and anthocyanin biosynthesis have been evaluated, and it is demonstrated that mutations with less severe effects on hypocotyl elongation show a similarly reduced effect on anthocyanin biosynthesis. These results are consistent with the cryptochrome photoreceptor mediating multiple regulatory pathways by the same primary mode of action.
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PMID:Mutations throughout an Arabidopsis blue-light photoreceptor impair blue-light-responsive anthocyanin accumulation and inhibition of hypocotyl elongation. 852 77

In cotyledons of etiolated mustard (Sinapis alba L.) seedlings, phytochrome-far-red-absorbing form-induced flavonoid biosynthesis was found to be inhibited by short-term ultraviolet (UV) irradiations. UV inhibition was shown for the synthesis of quercetin, anthocyanin, and also for the accumulation of the mRNA for chalcone synthase, the key enzyme of this pathway. The UV effect was more pronounced on flavonoid biosynthesis, a process that selectively occurs in the epidermal layers, than on the synthesis of mRNA for chlorophyll a/b-binding protein localized in the mesophyll tissue. These UV inhibitory effects were accompanied by cyclobutane pyrimidine dimer (CPD) formation showing a linear fluence-response relationship. CPD formation and UV inhibition of flavonoid biosynthesis was found to be partially reversible by blue/UV-A light via DNA photolyase (PRE), allowing photoreactivation of the DNA by splitting of CPDs, which are the cause of the UV effect. Like flavonoid formation PRE was also induced by the far-red-absorbing form of phytochrome and induction was inhibited by UV. A potential risk of inhibition, in response to solar UV-B irradiation, was shown for anthocyanin formation. This inhibition, however, occurred only if photoreactivation was experimentally reduced. The PRE activity present in the etiolated seedlings (further increasing about 5-fold during light acclimatization) appears to be sufficient to prevent the persistence of CPDs even under conditions of high solar irradiation.
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PMID:Ultraviolet Light Inhibition of Phytochrome-Induced Flavonoid Biosynthesis and DNA Photolyase Formation in Mustard Cotyledons (Sinapis alba L.). 1222 67

Influx of solar UV-B radiation (280-320 nm) will probably increase in the future due to depletion of stratospheric ozone. In plants, there are several targets for the deleterious UV-B radiation, especially the chloroplast. This review summarizes the early effects and responses of low doses of UV-B at the molecular level. The DNA molecules of the plant cells are damaged by UV due to the formation of different photoproducts, such as pyrimidine dimers, which in turn can be combatted by specialized photoreactivating enzyme systems. In the chloroplast, the integrity of the thylakoid membrane seems to be much more sensitive than the activities of the photosynthetic components bound within. However, the decrease of mRNA transcripts for the photosynthetic complexes and other chloroplast proteins are among very early events of UV-B damage, as well as protein synthesis. Other genes, encoding defence-related enzymes, e.g., of the flavonoid biosynthetic pathway, are rapidly up-regulated after commencement of UV-B exposure. Some of the cis-acting nucleotide elements and trans-acting protein factors needed to regulate the UV-induced expression of the parsley chalcone synthase gene are known.
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PMID:UV-B damage and protection at the molecular level in plants. 2431 Nov 38