Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

C factor B (Bf) is the key component of the C3 convertase of the alternative C pathway, and its gene resides in the class III region of the mammalian MHC. To elucidate the evolution of both the C system and the MHC, we isolated Bf cDNA clones from Xenopus laevis, an ectothermic vertebrate in which the MHC has been well defined at both the biochemical and functional levels. A part of the serine protease domain of the Xenopus Bf mRNA was amplified by reverse transcriptase-PCR, using degenerate primers corresponding to regions encoding the perfectly conserved amino acid sequences found in both the mouse Bf and C2 proteins. A full length Xenopus Bf cDNA clone was isolated from a Xenopus liver cDNA library. The deduced amino acid sequence of 747 residues showed the same domain structure as mammalian Bf and C2: three short consensus repeat domains, a von Willebrand domain and a serine protease domain. Xenopus Bf has 40% and 30% overall amino acid identity to mouse Bf and mouse C2, respectively. Because the amino acid identity between mouse Bf and mouse C2 is 38%, the gene duplication of Bf/C2 probably occurred before the divergence of amphibians and mammals. Southern blotting analysis of the Xenopus Bf gene showed a close linkage to the MHC, indicating that the Bf gene was linked to the class I and class II genes at the time Xenopus shared a common ancestor with mouse and man, 350 x 10(6) yr ago.
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PMID:Isolation of the Xenopus complement factor B complementary DNA and linkage of the gene to the frog MHC. 796 26

The conformation of the last 201 nucleotides located at the 3'-end of brome mosaic virus (BMV) RNAs was investigated in solution using different chemical and enzymatic probes. Bases were probed with dimethylsulfate (which methylates N-1 positions of A, N-3 positions of C and N-7 positions of G), a carbodiimide (which modifies N-1 positions of G and N-3 positions of U) and diethylpyrocarbonate (which modifies N-7 positions of A). Ribonucleases T1, U2 and S1 were used to map unpaired nucleotides and ribonuclease V1 to monitor paired bases or stacked nucleotides. Cleavage or modification sites were detected by gel electrophoresis either indirectly by analyzing DNA sequence patterns generated by primer extension with reverse transcriptase of the modified RNAs or by direct identification within the statistical cleavage patterns of the RNA. On the basis of these biochemical results, an atomic model was built by computer modeling and its stereochemistry refined. The deduced secondary structure of the RNA confirms data previously proposed by others but contains additional base-pairs (A27-U32, A28-G31, G41-A134, G64-C68, U80-A99, G81-A98, G88-U91, G100-U126, U104-U125, G162-G166 and A172-A191), one new tertiary long-range interaction (U103-U164) and a small triple helical conformation with (G41-A134)-A18 and (C42-G133)-A17 interactions. The new secondary structure also indicates the existence of a second pseudoknot involving pairing between residues A181 to A184 and residues U197 to U194, outside the domain conferring tyrosylation ability to BMV RNA. The main outcome from the model stems from its intricate folding, which allows a new assignment for the domains mimicking the anticodon- and D-loop regions of tRNA. Interestingly, the stem and loop region found structurally to be analogous to the anticodon arm of tRNA(Tyr) does not contain the tyrosine anticodon involved in the aminoacylation process. The structural analogies with canonical tRNA(Tyr) illustrate the functional mimicry existing between the BMV RNA structure and canonical tRNA(Tyr) that allows for their efficient aminoacylation by tyrosyl-tRNA synthetase. This structural model rationalizes mutagenic and footprinting data that have established the importance of specific regions of the viral RNA for recognition by its replicase, (ATP,CTP):tRNA nucleotidyl-transferase and yeast tyrosyl-tRNA synthetase. The new fold has biological implications that can be used as a predictive tool for elaborating new experiments.
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PMID:Solution structure of the 3'-end of brome mosaic virus genomic RNAs. Conformational mimicry with canonical tRNAs. 828 79

Recent identification of a C3-like gene in sea urchins revealed the presence of a complement system in invertebrates. To elucidate further the components and function of the pre-vertebrate complement system, we attempted to isolate an ascidian (urochordata) C3 convertase. After identification of C3 cDNA from Halocynthia roretzi, a Japanese ascidian, reverse transcriptase-PCR amplification of hepatopancreas RNA was performed using primers encoding highly conserved amino acid sequences of the vertebrate Bf and C2 serine protease domain. Two candidate sequences were identified, and the corresponding cDNA clones were isolated from a hepatopancreas library. Surprisingly, neither clone is related to Bf/C2 but rather share the same domain structure of mammalian C1r/C1s/MASP (mannan binding protein-associated serine protease), and are more related evolutionarily to mammalian MASP than to mammalian C1r or C1s. The identification of the tunicate MASP clones, amplified with primers designed to amplify Bf or C2, suggests that the lectin pathway antedated the classical and alternative pathways of complement activation.
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PMID:Ancient origin of the complement lectin pathway revealed by molecular cloning of mannan binding protein-associated serine protease from a urochordate, the Japanese ascidian, Halocynthia roretzi. 917 19