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

To examine the mechanism of recombination and the role of DNA repair in this process, we transfected a plasmid carrying duplicated copies of the Herpes simplex virus I thymidine kinase (Htk) gene, each containing an 8 bp XhoI site inserted in a unique site and with the neo coding for geneticin resistance located between them, into tk-deficient human cell lines which differ in their ability to carry out nucleotide excision repair. One parental cell line has a normal level of repair activity; the second has an intermediate level, and the third has virtually no repair activity. Several geneticin-resistant transfectant cell strains from each parental line were isolated and assayed for the ability to undergo productive recombination giving rise to tk+ cells. Approximately 25% of them could do so. Southern blot analysis of these transfectants indicated that the majority contained a single copy, or at most, two copies of the plasmid integrated into the chromosome. Fluctuation analysis tests to determine the rate of spontaneous recombination (events per 10(6) cells per cell generation) in the various cell strains showed that the rates ranged from 0.15 to 4.1. The mean rate for the cell strains derived from the repair-deficient cell line was 3.6; for those derived from the cells with an intermediate rate, it was 0.8; and for those with a normal rate of excision repair, it was 0.9. Southern blot analysis of tk+ recombinants showed that in all cases, one of the Htk genes had become wild-type, i.e., XhoI-resistant. 90% of the recombinants retained the Htk gene duplication, consistent with non-reciprocal transfer of genetic information, i.e., gene conversion. The rest contained a single, wild-type Htk gene, consistent with a single reciprocal exchange within a chromatid or a single unequal exchange between sister chromatids. These cell strains will be useful for investigating the role of DNA damage and repair in homologous recombination.
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PMID:Intrachromosomal homologous recombination in human cells which differ in nucleotide excision-repair capacity. 215 88

We have employed a retroviral vector, ZN(Smu/S gamma 2b)tk1, as a substrate for detecting the presence of immunoglobulin heavy chain constant region (CH) gene switch (S) recombination activity in murine pre-B cells. ZN(Smu/S gamma 2b)tk1 contains a neomycin (neo) resistance gene in addition to the herpes simplex virus thymidine kinase (Htk) gene which is positioned between murine Smu and S gamma 2b sequences. Stable acquisition of the ZN(Smu/S gamma 2b)tk1 vector was selected in G-418 and switch region recombination within these proviruses was selected by resistance to the drug bromodeoxyuridine (BUdR). Fluctuation analyses of ZN(Smu/S gamma 2b)tk1 infected 18-8tk- and 38B9tk- pre-B lines revealed Htk gene inactivations with apparent frequencies of 5 X 10(-5) and 1 X 10(-5) events/cell/generation, respectively, while G-418 resistant Ltk- fibroblasts lost the HTK phenotype at an apparent rate of 4 X 10(-8). Southern blot analysis demonstrated that switch recombination caused the deletion of the Htk gene in all pre-B clones examined while the loss of Htk in Ltk- clones was not mediated by S region recombination. In 21 out of 24 pre-B clones, the recombinations involved the tandemly repetitive portions of the Smu and S gamma 2b sequences. These results demonstrate that the CH gene S region segments inserted into ZN(Smu/S gamma 2b)tk1 are sufficient for B-cell-specific recombination/deletion within the S region tandem repeats.
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PMID:Immunoglobulin heavy chain switch region recombination within a retroviral vector in murine pre-B cells. 303 95