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

BAG1 is a small heat-shock protein of Toxoplasma gondii that is specifically expressed in the cyst-forming bradyzoite stage of the parasite. Upregulation of BAG1 mRNA occurs early during the differentiation pathway from tachyzoites to bradyzoites. In order define genomic elements involved in bradyzoite-specific gene regulation, chloramphenicol acetyltransferase (CAT)-reporter gene studies were performed with 5' flanking sequences of the BAG1 gene. Tachyzoites, transiently transfected with the BAG1/cat construct, exhibited very low CAT activity (200 fold less than in parasites transfected with a tubulin promoter/cat construct). After induction of bradyzoite differentiation by alkaline pH shift, however, CAT activity increased 50 fold, demonstrating bradyzoite-specific expression of the CAT reporter gene under control of 5' flanking sequences of BAG1. Stage-specific regulation of BAG1/CAT was independent of the 3'-flanking region, since constructs containing 3'-flanking sequences of the tachyzoite-specific SAG1 gene showed identical regulation to those containing the BAG1 3'-flanking region. The kinetics of BAG1/CAT induction in stably transfected parasites is similar to the kinetics of endogenous BAG1 expression: increased CAT activity was first detected on day 3 after alkaline pH shift (20 fold) and was dramatically upregulated 250 fold on day 4. A series of deletions in the BAG1 5'-flanking sequences demonstrated that a 324 nucleotide (nt) fragment, starting 60 nt upstream of the BAG1 transcription start, is sufficient to confer stage-specific regulation on the CAT reporter. These deletion analyses demonstrate that bradyzoite-specific expression of a heterologeous reporter gene requires only minimal genomic sequences.
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PMID:Bradyzoite-specific gene expression in Toxoplasma gondii requires minimal genomic elements. 910 51

Interphotoreceptor retinoid binding protein (IRBP), a putative component of the visual cycle, is expressed selectively in the retina and pineal gland. This study examined whether site-specific DNA hypomethylation plays a role in this expression regulation. Southern blotting of HpaII and MspI digests of DNA from various bovine and murine tissues (whole brain, retina, pineal gland, superior colliculus, cortex, thymus, habenular nucleus, cornea, liver, tail, and kidney) revealed that specific CpG dinucleotides in the IRBP gene promoter are hypomethylated in DNA from retinal photoreceptor cells and pineal gland compared to DNA from other tissues. These sites are methylated in DNA from non-photoreceptor retinal cells. Exogenous methylation of these sites diminished DNA:protein binding in electrophoretic mobility shift assays. HpaII methylation of chloramphenicol acetyltransferase reporter constructs suppressed IRBP but not SV40 promoter activity in transiently transfected primary cultures of embryonic chick retinal cells. These data indicate that specific cytosines in the bovine and murine IRBP promoters are unmethylated in photoreceptive cells but methylated in other tissues. This differential DNA methylation may modulate IRBP gene expression since exogenous methylation of the murine sites suppresses reporter gene transcription, apparently by inhibiting DNA:protein binding events.
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PMID:Site-specific DNA hypomethylation permits expression of the IRBP gene. 1113 9