Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ribonucleoprotein core of reovirus is a multienzyme complex that transcribes messenger ribonucleic acid (mRNA) from double-stranded RNA templates. So far, the core has resisted attempts to disassemble it and identify the polypeptide species responsible for RNA polymerase activity. As an alternative approach, we tested pyridoxal 5-phosphate (PLP) as a potential affinity labeling reagent for reovirus transcriptase in vitro; PLP has been used as an affinity reagent for cellular and viral nucleic acid polymerases. We found that PLP inhibited reovirus transcriptase reversibly (apparent Ki = 0.2 mM), but the inhibition was noncompetitive with respect to each of the four ribonucleoside triphosphates. This interaction required both the aldehyde and phosphate moieties in PLP, since pyridoxamine and pyridoxal were relatively inactive. To identify the polypeptides involved, we labeled the PLP--core complex by reductive alkylation with [3H]borohydride. At PLP concentrations close to the apparent Ki, labeling was selective for the two largest virion polypeptides, lambda 1 and lambda 2. At saturation, there were only 10 high-affinity PLP binding sites per core in each of the lambda polypeptide species. These findings implicate either or both lambda polypeptide species in viral transcription and they indicate that a special population, representing no more than 10% of the total lambda molecules in each core, participates in RNA synthesis.
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PMID:Pyridoxal phosphate as a probe of reovirus transcriptase. 735 41

Selenocysteine lyase (SCL) (EC 4.4.1.16) is a pyridoxal 5'-phosphate-dependent enzyme that specifically catalyzes the decomposition of L-selenocysteine to L-alanine and elemental selenium. The enzyme was proposed to function as a selenium delivery protein to selenophosphate synthetase in selenoprotein biosynthesis (Lacourciere, G. M., and Stadtman, T. C. (1998) J. Biol. Chem. 273, 30921-30926). We purified SCL from pig liver and determined its partial amino acid sequences. Mouse cDNA clones encoding peptides resembling pig SCL were found in the expressed sequence tag data base, and their sequences were used as probes to isolate full-length mouse liver cDNA. The cDNA for mouse SCL (mSCL) was determined to be 2,172 base pairs in length, containing an open reading frame encoding a polypeptide chain of 432 amino acid residues (M(r) 47, 201). We also determined the sequence of the N-terminal region of putative human SCL. These enzymes were shown to be distantly related in primary structure to NifS, which catalyzes the desulfurization of L-cysteine to provide sulfur for iron-sulfur clusters. The recombinant mSCL overproduced in Escherichia coli was a homodimer with the subunit M(r) of 47,000. The enzyme was pyridoxal phosphate-dependent and highly specific to L-selenocysteine (the k(cat)/K(m) value for L-selenocysteine was about 4,200 times higher than that for L-cysteine). Reverse transcriptase-polymerase chain reaction and Western blot analyses revealed that mSCL is cytosolic and predominantly exists in the liver, kidney, and testis, where mouse selenophosphate synthetase is also abundant, supporting the view that mSCL functions in cooperation with selenophosphate synthetase in selenoprotein synthesis. This is the first report of the primary structure of mammalian SCL.
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PMID:cDNA cloning, purification, and characterization of mouse liver selenocysteine lyase. Candidate for selenium delivery protein in selenoprotein synthesis. 1069 12