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)

We have isolated the mouse thrombospondin (TS) gene and determined the DNA sequence of the first nine exons and eight introns. Comparison with the human cDNA sequence reveals a high degree of conservation in coding sequences. Exon 3 of the mouse gene, which encodes the heparin-binding domain of TS, has a higher degree of nucleotide substitution than the other exons, but the distribution of charged and hydrophobic amino acids found in the human protein is generally conserved. DNA and protein sequences in exons 6-9, which encode a procollagen homology and motifs very similar to those found in at least two malarial parasite proteins, are highly conserved. The first two of the three malarial homologies in TS, which are also found in properdin and in components C6-9 of the lytic complement complex, are each encoded by a separate exon (8 and 9) in the mouse gene. Since the sequence data did not reveal substantial similarity in sequence between intron I in the human and mouse genes, we have reexamined the role of the first intron in the transcriptional regulation of the human TS gene. In accord with published studies (Laherty, C.D., Gierman, T.M., and Dixit, V.M. (1989) J. Biol. Chem. 264, 11222-11227), we find that deletion of some intronic segments from TS-chloramphenicol acetyltransferase (CAT) constructs reduces CAT activity in NIH 3T3 cells. However, deletion of the same sequences from TS-bovine growth hormone constructs does not affect the expression of bovine growth hormone in these cells. We conclude that differences in the activity of TS-CAT constructs reflect post-transcriptional differences that are peculiar to the resulting chimeric transcripts and that there is currently no evidence for a transcriptional enhancer in the first intron of the human TS gene.
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PMID:Characterization of the mouse thrombospondin gene and evaluation of the role of the first intron in human gene expression. 239 70

mRNA from normal Chinese hamster embryo (CHE) cells was transcribed to cDNA and subtracted with an excess of mRNA from Chinese hamster embryo cells transformed by nickel compounds. Here we report the recovery of a sequence found to be highly homologous to the mouse thrombospondin 1 gene that was obtained by this subtraction procedure. Since thrombospondin is antiangiogenic, cancer cells expressing high levels of thrombospondin cannot grow in vivo because capillaries will not proliferate to cells secreting thrombospondin. To examine expression of thrombospondin, normal CHE cells were stained with monoclonal antibodies to human thrombospondin. The protein was present abundantly in the cytoplasm of normal cells but at greatly reduced levels in Ni-transformed cells. Analysis of mRNA by Northern (RNA) blot revealed transcripts in normal cells but little thrombospondin mRNA in Ni-transformed cells. Loss of thrombospondin mRNA expression was related to Ni treatment rather than transformation, since Ni-resistant cells also exhibited fewer thrombospondin transcripts than did wild-type cells. Digestion of genomic DNA with various combinations of restriction enzymes revealed thrombospondin gene patterns that were identical in both cell types, suggesting that there were no major deletions or rearrangements of the gene in the nickel-transformed cells. The inactivation of the thrombospondin gene was further investigated by analyzing the promoter activity of this gene linked to a chloramphenicol acetyltransferase (CAT) reporter plasmid that was transfected into normal and Ni-transformed cells. The CAT activity in normal cells was significantly higher than in Ni-transformed cells, suggesting that the promoter region of thrombospondin was less efficiently transcribed in Ni-transformed cells. We studied the consequences of enhanced expression of the retinoblastoma (Rb) gene, a known tumor suppressor gene, on CAT transcription driven by the human thrombospondin promoter. Cotransfection of an expression vector containing the mouse Rb gene greatly enhanced the transcription from the thrombospondin promoter such that the expression was higher in normal cells than in transformed cells.
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PMID:Loss of thrombospondin transcriptional activity in nickel-transformed cells. 826 52