Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The most common mechanism of antibiotic resistance in multiply resistant Pseudomonas cepacia is decreased porin-mediated outer membrane permeability. In some gram-negative organisms this form of antibiotic resistance can be induced by growth in the presence of weak acids, such as salicylates, which suppress porin synthesis. To determine the effects of salicylates on outer membrane permeability of P. cepacia, a susceptible laboratory strain, 249-2, was grown in 10 mM sodium salicylate. Antibiotic susceptibility and uptake, as well as outer membrane protein patterns, were compared between strain 249-2 grown with and without salicylates. The MICs of chloramphenicol, trimethoprim, ciprofloxacin, and ceftazidime were compared between organisms grown in standard and salicylate-containing medium and are as follows: chloramphenicol, 12.5 versus 100 micrograms/ml; trimethoprim, 0.78 versus 3.125 micrograms/ml; ciprofloxacin, 0.4 versus 1.56 micrograms/ml; ceftazidime, 3.125 versus 3.125 micrograms/ml. The permeability of beta-lactam antibiotics was calculated from the rate of hydrolysis of the chromogenic cephalosporin, PADAC. There was no significant difference between strains grown in the presence and absence of salicylate. By using high-pressure liquid chromatography quantitation of loss from culture medium, the effect of 10 mM salicylate on the cellular permeability of chloramphenicol was measured in strain 249-2 by introduction of a plasmid which encodes production of chloramphenicol acetyltransferase. After 1 h of incubation, 18.5% +/- 1.54% versus 70.1% +/- 3.52%, and after 2 h, 4.20% +/- 1.65% versus 41.90% +/- 2.16% remained in supernatants from organisms grown in the absence and presence of 10 mM salicylate, respectively. Outer membrane protein pattern analysis demonstrated the absence of a protein of apparent molecular weight of 40,000 when strain 249-2 was grown in the presence of 10 mM salicylate. To determine whether this protein functioned as a porin, reconstituted membrane vesicles were constructed to assess antibiotic permeability. Vesicles constructed with this salicylate-suppressible outer membrane protein (OpcS) were permeable to chloramphenicol but not to penicillin G. These findings suggest that OpcS is a selective, antibiotic-permeable porin which can be suppressed by growth in the presence of salicylate. Further investigation will be required to determine the biochemical effects of salicylate on porin synthesis.
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PMID:Salicylate-inducible antibiotic resistance in Pseudomonas cepacia associated with absence of a pore-forming outer membrane protein. 128 56

To delineate the cis-acting element through which EBNA-2 transactivates latent membrane protein 1 (LMP1), we assayed the effect of EBNA-2 on the activity of LMP1 promoter upstream deletion mutants in the context of the LMP1 or heterologous promoters controlling chloramphenicol acetyltransferase (CAT) reporter gene expression in Epstein-Barr virus-negative Burkitt lymphoma cells. Assays of progressive 5' deletions of the LMP1 promoter revealed low constitutive and at least eightfold EBNA-2-stimulated activity from -512 to +40 (-512/+40), -334/+40, and -234/+40 LMP1CAT plasmids. More extensive 5'-deleted -205/+40, -155/+40, and -147/+40 LMP1CAT plasmids also had low constitutive activity but were not EBNA-2 responsive. The most 5'-deleted -55/+40 LMP1CAT plasmid had moderate constitutive activity and was not EBNA-2 inducible. Either orientation of the -334/+40 LMP1 sequence conferred EBNA-2 responsiveness when positioned upstream of an enhancerless simian virus 40 or herpes simplex virus thymidine kinase (TK) promoter. EBNA-2 and the cis-acting LMP1 DNA were both required to increase TK promoter-initiated mRNA, indicating that the EBNA-2 effect is at the transcriptional level. Further deletion analysis of the EBNA-2-responsive cis-acting element defined a -234/-92 LMP1 DNA fragment which conveyed EBNA-2 responsiveness to the herpes simplex virus TK promoter. The 5' 30 bp between -234 and -205 were essential for EBNA-2 responsiveness. Thus, these experiments define a 142-bp cis-acting element which is sufficient for conveying EBNA-2 responsiveness and an essential 30-bp component of that element. The role of this element in LMP1 and LMP2B expression and its possible role in LMP2A expression are discussed.
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PMID:Delineation of the cis-acting element mediating EBNA-2 transactivation of latent infection membrane protein expression. 165 73

A Haemophilus influenzae b (Hib) membrane protein with a molecular mass of 28 kDa bound polyclonal antisera raised against a highly purified Hib fimbrial subunit. We cloned the gene encoding this protein and found that the gene was expressed in Escherichia coli. DNA sequence analysis identified an 843-bp open reading frame which predicted a 26.78-kDa protein with an amino-terminal signal sequence and a mature protein with 70% similarity to the 28-kDa lipoprotein of E. coli (F. Yu, S. Inouye, and M. Inouye, J. Biol. Chem. 261:2284, 1986). Colony blot hybridization analysis with an intergenic probe of the cloned gene demonstrated that 29 of 32 H. influenzae strains hybridize with this gene. Insertion of a chloramphenicol acetyltransferase gene into the open reading frame inactivated expression of the 28-kDa protein in E. coli. Isogenic Hib strains were derived by marker exchange mutagenesis to generate mutants which no longer expressed the 28-kDa protein as recognized with Western immunoblot analysis. There was no difference in the rate of nasopharyngeal colonization of infant rats or monkeys by the isogenic mutants which lacked the 28-kDa protein compared with colonization by the wild-type strain. In contrast, the frequency of invasion and density of bacteremia in infant rats caused by the isogenic mutants were reduced relative to those caused by the wild-type Hib strain. We conclude that this 28-kDa outer membrane protein aids transepithelial invasion of type b strains but is not essential.
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PMID:Contribution of a 28-kilodalton membrane protein to the virulence of Haemophilus influenzae. 198 77

Epstein-Barr virus (EBV) latent-infection membrane protein (LMP) gene cis-acting regulatory sequences were assayed in human B lymphocytes by using chloramphenicol acetyltransferase (cat) gene expression as a reporter. The activities of progressively longer upstream elements from bases -55 to -2350 were compared. At least two positive cis-activating regulatory components (-155 to -147 and -234 to -205) upstream of the LMP promoter were defined. LMP promoter cat gene constructs were more active in a Burkitt's lymphoma cell line latently infected with the B95 EBV strain than in the same cells latently infected with the P3HR1 EBV strain. Since the P3HR1- and B95-infected cells differ in EBNA-2 and EBNA-LP expression, EBNA-2 or EBNA-LP is a likely transactivator of the LMP promoter. Probable cognate sequences for known transcription factors in the LMP promoter are discussed.
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PMID:cis-acting regulatory elements near the Epstein-Barr virus latent-infection membrane protein transcriptional start site. 215 69

We studied a clinical isolate of Salmonella typhi (strain 1895) characterized by resistance to 200 micrograms of chloramphenicol per ml despite the absence of chloramphenicol-inactivating activity. The outer membrane protein profile analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated a deficiency of one of the major protein species which may serve as a porin for entry of chloramphenicol. When the strain was transformed with a plasmid encoding chloramphenicol acetyltransferase, chloramphenicol added to the culture was not inactivated, suggesting a drastic reduction of permeability towards the drug. Moreover, transformants bearing a plasmid coding for the Escherichia coli OmpF porin became considerably more susceptible to chloramphenicol (40 micrograms/ml). On the other hand, transformants carrying a plasmid encoding the Salmonella typhi ompC gene remained as resistant to the drug as the parental strain, even though they overexpressed OmpC. These findings indicate that the lack of OmpF plays a major role in the resistance to chloramphenicol in strain 1895.
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PMID:Clinical isolate of a porinless Salmonella typhi resistant to high levels of chloramphenicol. 228 83

Several lines of evidence are compatible with the hypothesis that Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) or leader protein (EBNA-LP) affects expression of the EBV latent infection membrane protein LMP1. We now demonstrate the following. (i) Acute transfection and expression of EBNA-2 under control of simian virus 40 or Moloney murine leukemia virus promoters resulted in increased LMP1 expression in P3HR-1-infected Burkitt's lymphoma cells and the P3HR-1 or Daudi cell line. (ii) Transfection and expression of EBNA-LP alone had no effect on LMP1 expression and did not act synergistically with EBNA-2 to affect LMP1 expression. (iii) LMP1 expression in Daudi and P3HR-1-infected cells was controlled at the mRNA level, and EBNA-2 expression in Daudi cells increased LMP1 mRNA. (iv) No other EBV genes were required for EBNA-2 transactivation of LMP1 since cotransfection of recombinant EBNA-2 expression vectors and genomic LMP1 DNA fragments enhanced LMP1 expression in the EBV-negative B-lymphoma cell lines BJAB, Louckes, and BL30. (v) An EBNA-2-responsive element was found within the -512 to +40 LMP1 DNA since this DNA linked to a chloramphenicol acetyltransferase reporter gene was transactivated by cotransfection with an EBNA-2 expression vector. (vi) The EBV type 2 EBNA-2 transactivated LMP1 as well as the EBV type 1 EBNA-2. (vii) Two deletions within the EBNA-2 gene which rendered EBV transformation incompetent did not transactivate LMP1, whereas a transformation-competent EBNA-2 deletion mutant did transactivate LMP1. LMP1 is a potent effector of B-lymphocyte activation and can act synergistically with EBNA-2 to induce cellular CD23 gene expression. Thus, EBNA-2 transactivation of LMP1 amplifies the biological impact of EBNA-2 and underscores its central role in EBV-induced growth transformation.
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PMID:Epstein-Barr virus nuclear antigen 2 transactivates latent membrane protein LMP1. 235 28

The Epstein-Barr virus (EBV) BZLF1 gene product is thought to mediate the disruption of latent EBV infection. We have examined the regulatory effects of BZLF1 by studying its transactivating effects on seven different EBV promoters. We find that whereas the BZLF1 gene product increases the activity of the two early promoters, BMLF1 and BMRF1, it decreases the activity of three latent promoters (the BamHI-C and BamHI-W Epstein-Barr nuclear antigen promoters and the latent membrane protein promoter). The BZLF1-induced changes in promoter-directed chloramphenicol acetyltransferase activity occur in EBV-negative as well as EBV-positive cell lines and are accompanied by a similar change in chloramphenicol acetyltransferase mRNA. Deletion analysis of the BamHI Z fragment indicates that in a portion of the amino-terminal half of the BZLF1 gene product (amino acids 24 to 86) is not essential for positive transactivating effects but is required for down-regulating effects. Thus, different domains of the same EBV immediate-early gene product can either increase the function of EBV promoters active in productive infection or decrease the function of key promoters active in latent infection.
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PMID:The Epstein-Barr virus (EBV) BZLF1 immediate-early gene product differentially affects latent versus productive EBV promoters. 253 53

A 4-month-old infant with congenital heart disease and sepsis and arthritis, and subsequently meningitis, caused by an antibiotic-resistant strain of Haemophilus influenzae type b, failed to respond to sequential therapy with ampicillin and trimethoprim/sulfamethoxazole. Following treatment with ceftizoxime, the infant was well for 42 days, until he returned to the hospital and died. A total of 10 Haemophilus influenzae type b isolates, all outer membrane protein subtype 51, was isolated from the pretreatment blood and synovium, cerebrospinal fluid and subdural fluids, and the petrous pyramids at autopsy. Pretreatment isolates had no detectable plasmid DNA, chloramphenicol acetyltransferase or beta-lactamase; the minimal inhibitory concentration for ampicillin (AM) and chloramphenicol (CM) was 0.2 and 0.8 microgram/ml, respectively. However, all cerebrospinal fluid isolates had a 42-44 mD plasmid and produced chloramphenicol acetyltransferase and beta-lactamase; the minimal inhibitory concentration of these isolates to AM and CM were 12.5 and 25 micrograms/ml, respectively, and were also resistant to tetracycline and sulfonamide. Resistance to AM and CM was cotransferred by filter-mating conjugation at a frequency of one to two transconjugants per 10(5) to an Rd haemophilus recipient. Posttreatment isolates from the petrous pyramids also were resistant to AM and CM and produced chloramphenicol acetyltransferase and beta-lactamase activity, but had no plasmid DNA. These findings and data from genetic studies suggested that plasmid-bearing antibiotic-resistant Haemophilus influenzae type b was selected from a heterogenous population, and that the AM/CM resistance transposons were incorporated into the bacterial chromosome.
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PMID:Ampicillin-chloramphenicol-resistant Haemophilus influenzae: plasmid-mediated resistance in bacterial meningitis. 350 Apr 49

The human invariant chain (I gamma) of class II histocompatibility antigens spans the membrane of the endoplasmic reticulum once. It exposes a small amino-terminal domain on the cytoplasmic side and a carboxy-terminal, glycosylated domain on the exoplasmic side of the membrane. When the exoplasmic domain of I gamma is replaced by the cytoplasmic protein chloramphenicol acetyltransferase (CAT), CAT becomes the exoplasmic, glycosylated domain of the resulting membrane protein I gamma CAT. Deletion of the hydrophilic cytoplasmic domain from I gamma CAT gives rise to a secreted protein from which an amino-terminal segment is cleaved, most likely by signal peptidase. We conclude that the membrane-spanning region of I gamma contains a signal sequence in its amino-terminal half and that hydrophilic residues at the amino-terminal end of a signal sequence can determine cleavage by signal peptidase.
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PMID:The membrane-spanning segment of invariant chain (I gamma) contains a potentially cleavable signal sequence. 353 May

Chloramphenicol resistance in Haemophilus influenzae occurs most frequently via plasmid-mediated chloramphenicol acetyltransferase production. We studied four strains with high-level chloramphenicol resistance (MIC greater than 20 micrograms/ml) which did not have detectable chloramphenicol acetyltransferase activity. The chloramphenicol resistance determinant was transformed into a chloramphenicol-susceptible laboratory H. influenzae strain from each of the four wild-type strains, enabling isogenic comparisons. By thin-layer chromatography and a bioassay, there was no evidence of non-chloramphenicol acetyltransferase modification of chloramphenicol. In vitro protein synthesis in the presence of chloramphenicol was equivalently inhibited in the chloramphenicol-resistant transformants and in the susceptible recipient. Chloramphenicol uptake by these strains during logarithmic growth was compared by high-pressure liquid chromatographic quantitation; at chloramphenicol concentrations of 5, 10, and 20 micrograms/ml the four transformants showed a decreased rate of uptake of chloramphenicol compared with the isogenic chloramphenicol-susceptible recipient. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of outer membrane proteins revealed a markedly diminished 40-kilodalton protein in the resistant transformants. We propose that the mechanism of chloramphenicol resistance in these strains is a relative permeability barrier due to the loss of an outer membrane protein.
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PMID:A permeability barrier as a mechanism of chloramphenicol resistance in Haemophilus influenzae. 387 25


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