Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Apolipoprotein (apo) B exists in two forms, the full length protein apoB-100 and the carboxyterminal-truncated apoB-48 that is synthesized in the intestine due to editing of the apoB mRNA which generates a premature stop codon. To determine whether gene transfer of the catalytic subunit of the apoB mRNA editing enzyme APOBEC-1 (apoB mRNA editing enzyme catalytic polypeptide 1) into the liver of rabbits reconstitutes hepatic apoB mRNA editing and how this affects the plasma levels of apoB-containing lipoproteins, we constructed an APOBEC-1 recombinant adenovirus (Ad APOBEC-1). After injection of Ad APOBEC-1 into normal New Zealand White (NZW) or Watanabe heritable hyperlipidemic (WHHL) rabbits, up to 50% of the hepatic apoB mRNA was edited and freshly isolated hepatocytes secreted predominantly apoB-48-containing lipoproteins. VLDL isolated from Ad APOBEC-1-treated NZW and WHHL rabbits contained both apoB-100 and apoB-48, whereas that from control rabbits infected with a beta-galactosidase recombinant adenovirus (Ad LacZ) contained exclusively apoB-100. VLDL from WHHL rabbits treated with Ad APOBEC-1 had the same particle size, lipid composition, and content of apolipoprotein E as VLDL from Ad LacZ-infected control animals. An increase of VLDL was observed in NZW and WHHL rabbits after infection with Ad APOBEC-1 as well as Ad LacZ. After injection of Ad APOBEC-1, LDL became undetectable in the plasma of NZW rabbits and was reduced by an average of 65% in the plasma of WHHL rabbits compared to Ad LacZ-infected controls. LDL from Ad APOBEC-1-infected WHHL rabbits contained only apoB-100. VLDL isolated from Ad APOBEC-1-infected WHHL rabbits were rapidly cleared from the circulation after injection into NZW rabbits. These results provide further evidence that the switch in the hepatic synthesis from exclusively apoB-100 to partly apoB-48 can result in a reduction of LDL formation that requires the full-length apoB-100.
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PMID:Hepatic gene transfer of the catalytic subunit of the apolipoprotein B mRNA editing enzyme results in a reduction of plasma LDL levels in normal and watanabe heritable hyperlipidemic rabbits. 889 66

We describe a fusion transcript of Gal4 linked to its specific inhibitor protein Gal80 by 276 nucleotides of apolipoprotein (apo) B sequence as a selectable marker for mRNA editing. Editing of apoB mRNA is catalyzed by an editing enzyme complex that introduces a stop codon by deamination of C to U. The catalytic subunit APOBEC-1 is a cytidine deaminase and requires a second essential component recently cloned and termed APOBEC-1 complementing factor (ACF) or APOBEC-1-stimulating protein (ASP). The aim of this study was to demonstrate that APOBEC-1 plus ACF/ASP comprise all that is required for editing of apoB mRNA in vivo. Expression of APOBEC-1 and Gal4 fused to its inhibitor Gal80 by an intervening unedited apoB sequence (Gal4-apoB(C)-Gal80) did not result in the Gal4-dependent expression of HIS3 and beta-galactosidase in the yeast strain CG1945. Co-expression of APOBEC-1 and ACF/ASP induced editing of the apoB site in up to 13% of the Gal4-apoB(C)-Gal80 transcripts and enabled selection of yeast cells for robust expression of HIS3 and beta-galactosidase. Additional expression of the alternative splicing regulatory protein KSRP increased the editing of the apoB site by APOBEC-1 and ACF/ASP to 21%. Thus, APOBEC-1 and ACF/ASP represent the core apoB mRNA editing enzyme in vivo. This study demonstrates for the first time the successful use of a selectable marker for mRNA editing. The Gal4-Gal80 system is analogous to the two-hybrid assay and may have broader applications for the study of other mRNA processing reactions.
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PMID:Reconstitution of mRNA editing in yeast using a Gal4-apoB-Gal80 fusion transcript as the selectable marker. 1197 46

Activation-induced cytidine deaminase (AID) is indispensable for immunoglobulin maturation by somatic hypermutations and class switch recombination and is supposed to deaminate cytidines in DNA, while its homolog APOBEC-1 edits apolipoprotein (apo) B mRNA by cytidine deamination. We studied the editing activity of APOBEC-1 and AID in yeast using the selectable marker Gal4 linked to its specific inhibitor protein Gal80 via an apo B cassette (Gal4-C) or via the variable region of a mouse immunoglobulin heavy chain gene (Gal4-VH). Expression of APOBEC-1 induced C to U editing in up to 15% of the Gal4-C transcripts, while AID was inactive in this reaction even in the presence of the APOBEC-1 complementation factor. After expression of APOBEC-1 as well as AID approximately 10(-3) of yeast cells survived low stringency selection and expressed beta-galactosidase. Neither AID nor APOBEC-1 mutated the VH sequence of Gal4-VH, and consequently the yeast colonies did not escape high stringent selection. AID, however, induced frequent plasmid recombinations that were only rarely observed with APOBEC-1. In conclusion, AID cannot substitute APOBEC-1 to edit the apo B mRNA, and the expression of AID in yeast is not sufficient for the generation of point mutations in a highly transcribed Gal4-VH sequence. Cofactors for AID induced somatic hypermutations of immunoglobulin variable regions, that are present in B cells and a variety of non-B cells, appear to be missing in yeast. In contrast to APOBEC-1, AID alone does not exhibit an intrinsic specificity for its target sequences.
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PMID:The cytidine deaminases AID and APOBEC-1 exhibit distinct functional properties in a novel yeast selectable system. 1596 68