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

---

Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prolyl 4-hydroxylase, an alpha 2 beta 2 tetramer, catalyzes the formation of 4-hydroxyproline in collagens and related proteins by hydroxylating proline residues in peptide linkages. The beta-subunit of prolyl 4-hydroxylase (P4HB) is a highly unusual multifunctional polypeptide that is identical to the enzyme protein disulfide isomerase and a major cellular thyroid hormone-binding protein and is highly similar to a glycosylation site-binding polypeptide of oligosaccharyl transferase. We report here the regional assignment of the gene for this multifunctional polypeptide. In situ hybridization mapped the gene to 17q25. Southern blot analyses of restricted DNA from a chromosome-mediated gene transfer transfectant panel suggested that the P4HB gene is located distal to the gene for thymidine kinase, either between the genes for thymidine kinase and galactokinase or on the telomeric side of both these genes.
...
PMID:Regional assignment of the human gene coding for a multifunctional polypeptide (P4HB) acting as the beta-subunit of prolyl 4-hydroxylase and the enzyme protein disulfide isomerase to 17q25. 164 89

A mouse L cell line containing the centromeric insertion of herpes thymidine kinase genes (tk) was previously shown to undergo a high frequency of DNA rearrangement at the site of tk insertion. Analysis of TK- revertants had demonstrated that DNA rearrangements were usually associated with DNA deletion and were always mediated by intrachromosomal recombinations. In this study, we further analyzed several TK+ subclones to examine the mode of DNA rearrangements in the absence of negative selection pressure. In two clones, LC2-3F and LC2-3E17, rearrangements were accompanied by DNA amplification and were mediated by intrachromosomal recombination. In subclone LC2-3E17-19, we further detected perturbations in the pattern of centromeric heterochromatization. This was associated with chromosome instability, as evidenced by chromosome breakage at the centromere. The analysis of three other sibling clones, LC2-3, LC2-6 and LC2-15, further suggests that reciprocal recombination events may play a role in such centromeric rearrangements. These results suggest that DNA rearrangements in the centromere may be mediated by a number of different mechanisms, and generally do not affect chromosome stability except when accompanied by changes in the pattern of heterochromatization.
...
PMID:Chromosomal recombination and breakage associated with instability in mouse centrometric satellite DNA. 260 Sep 68

The JY328 clone was identified in a human genomic library using cDNA corresponding to mRNA for HLA-B7 as a probe. The L/328 cell line was established by cotransformation of mouse Ltk- cells with the herpes thymidine kinase gene and clone JY328. On Northern blots, RNA from L/328 strongly hybridized to an HLA class I probe, and an antigen was recognized by an anti-HLA class I framework antibody on the cell surface. A DNA probe corresponding to a segment of intron 7 was developed by comparing the nucleotide sequence of clone JY328 with that of other HLA class I-type genes. Using the radiolabeled probe to screen Southern blots of DNA from families with siblings exhibiting intra-HLA recombinations, a restriction fragment length polymorphism was revealed--a 1.4 kb BstE II band not present in all individuals. A corresponding fragment was apparent in the base sequence of clone JY328. The occurrence of this band on Southern blots established that JY328 maps distinct from and centromeric to the HLA-C locus and near to the HLA-B locus. Antibody absorption studies and cytotoxicity tests indicated that the JY328 gene product was not an HLA-B antigen but that it did specifically absorb CW7-specific antibody. In sum, these results suggest a novel, polymorphic HLA class I gene which expresses a product serologically similar to HLA-Cw7 but which does not map within the corresponding locus.
...
PMID:HLA-JY328: mapping studies and expression of a polymorphic HLA class I gene. 300 45

The human peroxisome proliferator activated receptor (hPPAR) was cloned from a human liver cDNA library. The cDNA exhibited 85% and 91% DNA and deduced amino acid sequence identity with mouse PPAR (mPPAR), respectively. The hPPAR gene was mapped on human chromosome 22 slightly telomeric to a linkage group of six genes and genetic markers that are located in the general region 22q12-q13.1. Cotransfection assays of mouse Hepa 1 cells were used to roughly compare the ability of hPPAR- and mPPAR-expressed cDNAs to trans-activate the acyl CoA oxidase (ACO) PPAR response element located 5' upstream to the minimal thymidine kinase promoter driving the expression of the chloramphenicol acetyl transferase (CAT) reporter gene. Both receptors elicited a response with the prototypical peroxisome proliferators nafenopin, clofibrate, and WY-14,643. Moreover, using cotransfection assays in which the CAT reporter plasmid contained the CYP4 A6 gene response element rather than the ACO element, it was shown that hPPAR is capable of very efficiently trans-activating a second PPAR response element. These results indicate that the PPAR is present in humans in a form that is functional and can trans-activate response elements derived from two different genes, the rat ACO and the rabbit CYP4A6.
...
PMID:cDNA cloning, chromosomal mapping, and functional characterization of the human peroxisome proliferator activated receptor. 768 26

A human x Chinese hamster (CH) somatic cell hybrid subclone deficient in HPRT and containing only human chromosome 18 was irradiated with 7000 rad and fused to a thymidine kinase deficient CH cell line. Radiation-rescued hybrid cell lines, selected in HAT medium, were analyzed for human DNA with human interspersed-repeat sequence primers. Size and number of human chromosome fragments retained in a subset of hybrids were determined by FISH. A panel of 98 radiation hybrids (RH) was selected and analyzed for 90 chromosome 18-specific STSs by PCR, and for the D18Z1 centromeric marker by Southern blotting. STSs were developed from previously mapped RFLP loci and from published sequences. In addition, 32 novel STSs were generated from an 18-specific lambda library and from 18-specific YACs previously localized to chromosome bands by FISH. Marker retention frequency varied from 8-65% with an average of 24%. In selected RH the STS typing data were correlated with the chromosome 18 regions retained using 'reverse FISH' of IRS-PCR products from the RH to normal metaphase chromosomes. The order and intermarker distances of loci were determined using two-point and multipoint maximum likelihood methods. The resulting RH map covers most of chromosome 18 with four groups of tightly linked markers and three regions of loosely linked markers, one around the centromere and two on the long arm. More than a third of the markers are polymorphic and allow integration with the linkage map. This RH map provides a framework for establishing a clone contig of the entire chromosome 18.
...
PMID:A radiation hybrid map of human chromosome 18. 812 19

African trypanosomes undergo antigenic variation of their variant surface glycoprotein (VSG) coat to avoid being killed by their mammalian hosts. The active VSG gene is located in one of many telomeric expression sites. Replacement of the VSG gene in the active site or switching between expression sites can give rise to a new VSG coat. To study Trypanosoma brucei VSG expression site inactivation rather than VSG gene switching, it is useful to have an in vitro negative-selection system independent of the VSG. We have achieved this aim by using a viral thymidine kinase (TK) gene. Following integration of the TK gene downstream of the 221a VSG expression site promoter, transformant cell lines became sensitive to the nucleoside analog 1-(2-deoxy-2-fluoro-8-D-arabinofuranosyl)-5-iodouracil. These TK trypanosomes were able to revert to resistance at a rate approaching 10(-5) per cell per generation. The majority of revertants expressed a new VSG gene even though there had been no selection against the VSG itself. Analysis of these switched variants showed that some had shut down TK expression via an in situ expression site switch. However, most variants had the complete 221 expression site deleted and another VSG expression site activated. We speculate that a new VSG expression site cannot switch on without inactivation of the old site.
...
PMID:Frequent loss of the active site during variant surface glycoprotein expression site switching in vitro in Trypanosoma brucei. 941 67

The addition of new telomeres to the ends of broken chromosomes, termed chromosome healing, has been extensively studied in unicellular organisms; however, its role in the mammalian cell response to double-strand breaks is unknown. A system for analysis of chromosome healing, which involves the integration of plasmid sequences immediately adjacent to a telomere, has been established in mouse embryonic stem cells. This "marked" telomere contains a neo gene for positive selection in G418, an I-SceI endonuclease recognition sequence for introducing double-strand breaks, and a herpes simplex virus thymidine kinase gene for negative selection with ganciclovir for cells that have lost the telomere. Transient expression of the I-SceI endonuclease results in terminal deletions involving telomeric repeat sequences added directly onto the end of the broken chromosome. The sites of addition of the new telomeres contain short regions of complementarity to telomeric repeat sequences. The most common site of addition is the last A of the ATAA 3' overhang generated by the I-SceI endonuclease, without the loss of a single nucleotide from the end of the chromosome. The next most frequent site involved 5 bp of complementarity, which occurred after the loss of four nucleotides from the end of the chromosome. The new telomeres are generally much shorter than in the parental cell line, and most increase in size with time in culture. These results demonstrate that chromosome healing is a mechanism for repair of chromosome breaks in mammalian cells.
...
PMID:Chromosome healing in mouse embryonic stem cells. 1035 89

Allelic loss is an important mutational mechanism in human carcinogenesis. Loss of heterozygosity (LOH) at an autosomal locus is one outcome of the repair of DNA double-strand breaks (DSBs) and can occur by deletion or by mitotic recombination. We report that mitotic recombination between homologous chromosomes occurred in human lymphoid cells exposed to densely ionizing radiation. We used cells derived from the same donor that express either normal TP53 (TK6 cells) or homozygous mutant TP53 (WTK1 cells) to assess the influence of TP53 on radiation-induced mutagenesis. Expression of mutant TP53 (Met 237 Ile) was associated with a small increase in mutation frequencies at the hemizygous HPRT (hypoxanthine phosphoribosyl transferase) locus, but the mutation spectra were unaffected at this locus. In contrast, WTK1 cells (mutant TP53) were 30-fold more susceptible than TK6 cells (wild-type TP53) to radiation-induced mutagenesis at the TK1 (thymidine kinase) locus. Gene dosage analysis combined with microsatellite marker analysis showed that the increase in TK1 mutagenesis in WTK1 cells could be attributed, in part, to mitotic recombination. The microsatellite marker analysis over a 64-cM region on chromosome 17q indicated that the recombinational events could initiate at different positions between the TK1 locus and the centromere. Virtually all of the recombinational LOH events extended beyond the TK1 locus to the most telomeric marker. In general, longer LOH tracts were observed in mutants from WTK1 cells than in mutants from TK6 cells. Taken together, the results demonstrate that the incidence of radi-ation-induced mutations is dependent on the genetic background of the cell at risk, on the locus examined, and on the mechanisms for mutation available at the locus of interest.
...
PMID:Different mechanisms of radiation-induced loss of heterozygosity in two human lymphoid cell lines from a single donor. 1122 43

Chromosome instability plays an important role in cancer by promoting the alterations in the genome required for tumor cell progression. The loss of telomeres that protect the ends of chromosomes and prevent chromosome fusion has been proposed as one mechanism for chromosome instability in cancer cells, however, there is little direct evidence to support this hypothesis. To investigate the relationship between spontaneous telomere loss and chromosome instability in human cancer cells, clones of the EJ-30 tumor cell line were isolated in which a herpes simplex virus thymidine kinase (HSV-tk) gene was integrated immediately adjacent to a telomere. Selection for HSV-tk-deficient cells with ganciclovir demonstrated a high rate of loss of the end these "marked" chromosomes (10-4 events/cell per generation). DNA sequence and cytogenetic analysis suggests that the loss of function of the HSV-tk gene most often involves telomere loss, sister chromatid fusion, and prolonged periods of chromosome instability. In some HSV-tk-deficient cells, telomeric repeat sequences were added on to the end of the truncated HSV-tk gene at a new location, whereas in others, no telomere was detected on the end of the marked chromosome. These results suggest that spontaneous telomere loss is a mechanism for chromosome instability in human cancer cells.
...
PMID:The relationship between spontaneous telomere loss and chromosome instability in a human tumor cell line. 1122 47

Cisplatin (CDDP) resistance is one of the major impediments in cancer chemotherapy. In an attempt to define this complex mechanism(s) of resistance, we have identified 7 cDNA fragments which are overexpressed in CDDP resistant small cell lung cancer cell line (SR-2) using PCR selected cDNA subtraction. One of these fragments was identical with nucleotide 3657-4042 of MRP4. The other fragments share sequence homology with elongation factor alpha, human placenta villi cDNA, heat shock protein (Hsp70), ribosomal RNA, BNP1 brain specific Na-dependent inorganic phosphate cotransporter and telomeric catalytic subunit. Examination of other MRP members (MRP1, 2, 3, 5, 6) did not show discernable differences in their expression between the parental (SCLC1) and the CDDP-resistant variant (SR-2). Full length MRP4 cDNA was obtained from SCLC1 and SR-2. Both cell lines carry a point mutation at nucleotide 3532 while SR-2 carries two additional mutations at 3228 and 3246. Since MRP4 is known to transport azidiothymidine (AZT) and overexpression of MRP4 confers AZT resistance, we have studied growth inhibitory effects of AZT and [3H]-AZT accumulation. Interestingly, SR-2 is more sensitive to AZT while accumulating lesser amounts of [3H]-AZT. The thymidine kinase activity is similar in both cell lines. Thus, the increased sensitivity to AZT in SR-2 could not be solely due to mutation of MRP4. These findings are most likely due to the inhibitory effects of telomere catalytic subunit by AZT. Thus, certain biochemical changes induced by CDDP can be explored for future treatment to overcome this form of resistance.
...
PMID:Overexpression of mutated MRP4 in cisplatin resistant small cell lung cancer cell line: collateral sensitivity to azidothymidine. 1279 91


1 2 Next >>

---