Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two genes, HEXA and HEXB, encode the alpha- and beta-subunits, respectively, of human beta-hexosaminidase. In the mouse, the corresponding genes are termed Hexa and Hexb. The subunits dimerize to yield three isozymes, beta-hexosaminidase A (alpha beta), B (beta beta), and S (alpha alpha), that have the capacity to degrade a variety of substrates containing beta-linked N-acetylglucosamine and N-acetylgalactosamine residues. Mutations in the HEXA or HEXB gene resulting in a beta-hexosaminidase deficiency cause Tay-Sachs or Sandhoff disease, respectively. As a prelude to the creation of mouse models of these lysosomal storage diseases, we have characterized the molecular biology of the mouse beta-hexosaminidase system. Protein sequences derived from the cloned Hexa and Hexb cDNAs were 55% identical to each other and were also very similar to the cognate human sequences: 84% sequence identity with human HEXA and 75% with HEXB. The mouse hexosaminidase subunits, when expressed in HeLa cells from the cDNAs, displayed specificity toward synthetic substrates similar to the human subunits. The Hexa and Hexb genes were 25 and 22 kb in length, respectively. Each gene was divided into 14 exons, with the positions of introns precisely matching those of the corresponding human genes. The 5' flanking regions of the mouse genes demonstrated promoter activity as ascertained by their ability to drive chloramphenicol acetyltransferase gene expression in transfected NIH 3T3 cells. The sequences of these regulatory regions were G+C-rich in the 200 bp upstream of the respective initiator ATGs. Several putative promoter elements were present, including Sp1, AP2, CAAT, and TATA motifs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Structure and expression of the mouse beta-hexosaminidase genes, Hexa and Hexb. 795 36

Glucosidase I initiates the processing of asparagine (N-) linked glycoproteins by removing the distal alpha1,2-linked glucosyl residue of the tetradecasaccharide Glc(3)Man(9)GlcNAc(2). The gene encoding this enzyme was isolated and its structural organization and promoter activity determined. The major transcript for glucosidase I on northern blot appeared to be 3.1 kb; Southern blotting and DNA sequencing indicated the size of the gene to be 6.8 kb, comprising four exons separated by three introns. The first exon encodes the cytoplasmic tail and transmembrane domain; the fourth encodes the putative catalytic domain of the enzyme. Exon-intron junctions are flanked by consensus splice donor and acceptor sequences. Transcription initiation sites were mapped by primer extension, ribonuclease protection assay and RT-PCR analysis. Primer extension results showed multiple initiation sites at -150, -156, and -272 bp relative to the translation initiation codon ATG. Sequence analysis of 5' flanking region showed no canonical TATA box, a high GC content, Sp1 and ETF binding sites (typical of a housekeeping gene promoter). Also noteworthy, the promoter region contains several generic STAT factor binding sites, one nearly perfect, and two half GR binding elements. Other cis- acting elements recognized by transcription factors such as AP-2, NF-kappaB, estrogen receptor, and progesterone receptor (PR) were also present in the putative promoter region. To determine the promoter activity, a construct encompassing the region between -2114 to -5 bp of the putative promoter was ligated to the chloramphenicol acetyltransferase (CAT) reporter plasmid and transiently transfected into COS 7 cells. CAT assay results clearly show transcriptional activity of the promoter.
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PMID:Genomic organization and promoter activity of glucosidase I gene. 1040 45

The X protein of hepatitis B virus (HBx) plays a major role on hepatocellular carcinoma (HCC). Apolipoprotein B (apoB) in the liver is an important glycoprotein for transportation of very low density lipoproteins and low density lipoproteins. Although lipid accumulation in the liver is known as one of the factors for the HCC, the relationship between HBx and apoB during the HCC development is poorly understood. To better understand the biological significance of HBx in HCC, liver Chang cells that specifically express HBx were established and characterized. In this study we demonstrate that overexpression of HBx significantly up-regulates the expression of UDP-N-acetylglucosamine:beta-d-mannoside-1,4-N-acetylglucosaminyltransferase-III (GnT-III), an enzyme that functions as a bisecting-N-acetylglucosamine (GlcNAc) transferase in apoB, and increases GnT-III promoter activity in a chloramphenicol acetyltransferase assay. GnT-III expression levels of HBx-transfected cells appeared to be higher than that of hepatocarcinoma cells as well as GnT-III-transfected cells, indicating that HBx may has a strong GnT-III promotor-enhancing activity. Intracellular levels of apoBs, which contained the increased bisecting GlcNAc, were accumulated in HBx-transfected liver cells. These cells as well as GnT-III-transfected liver cells revealed the inhibition of apoB secretion and the increased accumulation of intracellular triglyceride and cholesterol compared with vector-transfected cells. Moreover, overexpression of GnT-III and HBx in liver cells was shown to down-regulate the transcriptional level of microsomal triglyceride transfer protein, which regulates the assembly and secretion of apoB. Therefore, our study strongly suggested that the HBx increase in intracellular accumulation of aberrantly glycosylated apoB resulted in inhibition of secretion of apoB as well as intracellular lipid accumulation by elevating the expression of GnT-III.
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PMID:The hepatitis B virus X protein inhibits secretion of apolipoprotein B by enhancing the expression of N-acetylglucosaminyltransferase III. 1512 6