Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A number of HSV-2 isolates, sequentially recovered from ulcerative ano-genital lesions of an AIDS patient during a prolonged treatment with acyclovir (ACV), have been studied at the molecular level. All of them were highly resistant to ACV (ACV-r) and shown to be virtually deficient in thymidine kinase (TK) activity. The ACV-r phenotype was demonstrated to be due to the production of truncated TK polypeptide. Structural alteration of this gene, as shown in one isolate, was caused by a chain-terminating mutation that originated from a cytidine deletion at position 520 of the TK open reading frame. This mutation generated a TGA stop codon 27 nucleotides downstream. An additional isolate was also recovered following ACV discontinuation and after a cycle of treatment with foscarnet. This isolate had lost the ACV-r trait and was characterized by a wild type TK sequence and by the production of a functional enzyme. Data presented confirm that a prolonged treatment with acyclovir can easily select ACV-r HSV-2 isolates carrying a TK- phenotype caused by a frameshift mutation. Although recovered from lesions tributary of different myelomers, these isolates may belong to the same strain that has undergone multiple cycles of reactivation and has possibly mutated during its axonal route to the skin.
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PMID:A point mutation in the thymidine kinase gene is responsible for acyclovir-resistance in herpes simplex virus type 2 sequential isolates. 132 74

DNA from Cotia virus, an unclassified poxvirus, was mapped by overlapping fragment analysis using the restriction endonucleases HindIII, PstI, BamHI, XhoI, SalI, and SmaI. The linear genome was 177 kbp in length and possessed inverted terminal repeats and cross-links. A Cotia virus thymidine kinase (TK) gene was detected and mapped to about 74 kbp from the left end of the genome using degenerate oligonucleotide probes. Nucleotide sequencing of the TK gene revealed an open reading frame (ORF) that encoded a peptide of 178 amino acids. An A/T-rich sequence, TAA AAA TGA ATA AATA, and a transcription termination signal, TTTTTGT, were revealed upstream and just downstream of the ORF, respectively, consistent with the characteristic features of an early poxvirus gene. Cotia virus resembles swinepox virus based on the restriction profiles generated by endonucleases and shares amino acid sequence similarity with orthopox, leporipox, Yaba, and fowlpox viruses.
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PMID:Unclassified poxvirus: characterization and physical mapping of Cotia virus DNA and location of a sequence capable of encoding a thymidine kinase. 779 81

Three non-sense mutants of varicella-zoster virus (VZV) thymidine kinase (TK) gene, VZTK325, VZTK278 and VZTK224, were isolated. The mutants had a single nucleotide substitution at codons 326, 279 and 225, which changed the codon of TGG (tryptophan) to the stop codon TGA. The wild type (WT) and mutant TKs were expressed in E. coli cells and their characteristics were evaluated. VZTK224 lost TK activity, but VZTK325 and VZTK278 maintained 74.8% and 21.2% of the WT TK activity. On the other hand, all mutants lost the thymidylate kinase activity. Moreover, VZTK325 and VZTK278 polypeptides were heat-labile. These data suggest that the carboxy-terminal portion of herpesvirus TK plays an important role in the stable folding of TK and thymidylate kinase activity.
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PMID:Analysis of the non-sense mutants of varicella-zoster virus thymidine kinase. 941 14

Nerve growth factor differentiates precursor cells into sympathetic neurons. Does acquisition of a "neuronal" phenotype after nerve growth factor involve biosynthesis of chromogranin A, the major soluble protein in chromaffin granule cores? Nerve growth factor activated chromogranin A gene expression 7.6-fold in PC12 pheochromocytoma cells, and similarly activated PC12-transfected mouse, rat or human chromogranin A promoter/reporter constructs. Chromogranin A promoter 5'-deletions narrowed the nerve growth factor response element to a region from - 77 to - 61 bp upstream of the cap site, a region containing the chromogranin A cyclic AMP response element (TGACGTAA). Three different site-directed mutations of the cyclic AMP response element each reduced the nerve growth factor effect by >90%. Transfer of the cyclic AMP response element to a heterologous (thymidine kinase) promoter activated that promoter approximately 5-fold after nerve growth factor, while transfer of a cyclic AMP response element point-gap mutant (TGA-GTAA) to a heterologous promoter abolished the nerve growth factor effect. These findings indicate that the cyclic AMP response element in cis is, at least in part, both necessary and sufficient to activate the chromogranin A gene. Chemical blockade of the nerve growth factor receptor TrkA or the mitogen-activated protein kinase pathway component MEK substantially diminished nerve growth factor-induced expression of chromogranin A. By contrast, the response of chromogranin A to nerve growth factor was not impaired after blockade of phospholipase C-gamma or phosphoinositide-3 kinase. Chemical blockade of TrkA, Ras, MEK or mitogen-activated protein kinase similarly inhibited nerve growth factor activation of chromogranin A. Expression of constitutively activated Ras, Raf or MEK mutants increased chromogranin A promoter activity. Expression of dominant negative (inhibitory) mutants of Sos, Ha-Ras, Rafl, mitogen-activated protein kinase, ribosomal protein S6 serine kinase II (CREB kinase) or CREB (KCREB) each inhibited the nerve growth factor-induced increase in chromogranin A promoter activity. Thus, each component of the mitogen-activated protein kinase pathway is crucially involved in relaying the nerve growth factor signal in trans to the chromogranin A gene, in the following proposed sequence: nerve growth factor --> TrkA --> Shc/Grb2/Sos --> Ras --> Raf --> MEK --> mitogen-activated protein kinase --> ribosomal protein S6 serine kinase II --> CREB cyclic AMP response element.
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PMID:Neurotrophin activation of catecholamine storage vesicle protein gene expression: signaling to chromogranin a biosynthesis. 1019 63

Seven herpes simplex type-1 (HSV-1) isolates from herpes simplex keratitis (HSK) cases clinically resistant to acyclovir (ACV) were analyzed for the mechanism of ACV resistance in them. The purpose of the study was to focus the attention of ophthalmologists on the frequency of occurrence of ACV resistance in HSK and to characterize such a phenomenon. We employed in-vitro plaque reduction assay, thymidine kinase assay, polymerase chain reaction, single-strand confirmation polymorphism analysis and sequencing to detect any mutation(s) in thymidine kinase gene in this analytical study. Four of the seven HSV-1 isolates proved ACV resistant by plaque reduction assay and three of them showed reduced thymidine kinase activity. Altered mobility pattern indicative of mutation within 335 base pair PCR product bracketing the suggested homopolymer mutational hotspot (7 Guanosine) was detected in 2 of these 3 isolates. DNA sequencing showed a deletion at nucleotide position 336 from the tk gene transcription start in both the isolates. This mutation has generated the first TGA stop codon 27 nucleotides downstream in the tk open reading frame. Our study also suggests the need of clinical/molecular surveillance of ACV resistance in HSV types in a given geographic location for better management of HSV infections.
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PMID:Acyclovir resistance in herpes simplex virus isolates from keratitis cases: an analysis from a developing country. 1083 67