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:3.1.30.2 (endonuclease)
18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Gel shift assays have been employed to examine the association of the thyroid hormone receptor with specific DNA sequences in the 5'-flanking DNA of the rat growth hormone (rGH) gene. This DNA is known to have structure(s) that mediate thyroid hormone effects on the rGH promoter. The receptors used were obtained from preparations purified 300-500-fold from rat liver nuclear extracts and contained about 1% pure receptors. Thyroid hormone receptor binding to DNA was assessed by monitoring protein-bound 32P-labeled restriction endonuclease fragments in parallel with L-tri[125I]iodothyronine-labeled protein-DNA complexes. The receptors were found to bind specifically to four different regions of the rGH 5'-flanking DNA (nucleotides -1730 to -1230, -530 to -230, -181 to -149, and -149 to +12) numbered with respect to the transcriptional start site. The specificity of the binding was documented by the finding that the receptor did not bind to other rGH 5'-flanking DNA sequences or to several other DNAs and by the fact that only the DNAs exhibiting specific binding could block the binding of radiolabeled DNA. The binding was also detected in NaCl concentrations up to 140 mM, reduced by Mg2+ concentrations up to 5 mM, and inhibited by 1 mM zinc. The DNA sequence-specific binding of the receptor was found to require occupancy of the receptor by the hormone (L-triiodothyronine) and could also be observed when the receptor was occupied by the thyroid hormone antagonist amiodarone. These results indicate that thyroid hormone receptors interact specifically with several sites on the 5'-flanking DNA of the rGH gene and that hormone occupancy is not required for the binding. Thus, thyroid hormone may act by stimulating a transcriptional activation function of the receptor rather than by stimulating DNA binding per se.
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PMID:The thyroid hormone receptor binds to multiple domains of the rat growth hormone 5'-flanking sequence. 283 88

T4-binding globulin (TBG) is a glycoprotein of hepatic origin which transports thyroid hormone in serum. Inherited TBG defects in man are X-chromosome linked and are expressed in hemizygotes as complete deficiency, partial deficiency, or excess. Since TBG is not necessary for thyroid hormone action, affected subjects are healthy. Using DNA probes for human TBG, we searched for restriction fragment length polymorphisms in six affected males belonging to 6 unrelated families with inherited complete TBG deficiency and an equal number of normal males. TBG could not be detected in the serum of any of the TBG-deficient males by a specific and sensitive RIA capable of detecting as little as 5 micrograms TBG/L or 0.031% of the average normal serum TBG concentration. DNA isolated from white blood cells was digested with 11 restriction endonucleases, and the digests were submitted to DNA blot analysis using two cloned TBG-DNA probes which together covered the entire protein coding and the 5'-flanking sequences of the TBG gene. A total of 26 different bands were detected on DNA blots, identifying 18 restriction sites located within the 4.2-kilobase TBG gene, which includes intronic, exonic, and 5'-flanking sequences. This analysis, which sampled 2.3% of the total TBG genome, failed to reveal differences in fragment size among the 6 TBG-deficient and 6 normal males examined. One restriction endonuclease (NcoI) identified normal sequences at the putative promoter region of the gene, and four other endonucleases (TaqI, SstII, MspI, and HpaII) recognized the cytosine-guanine dinucleotide phosphate sequences representing potential mutation hot spots. Although C was methylated at these sites, no C to T (thymidine) transitions were found. These data suggest that large deletions, insertions, or rearrangements of the TBG gene, or mutations at sites of methylated cytosine-guanine dinucleotide phosphate dimers are not common mechanisms for inherited complete TBG deficiency in man.
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PMID:Detection of the thyroxine-binding globulin (TBG) gene in six unrelated families with complete TBG deficiency. 290 29

A cDNA clone containing sequences complementary to the mRNA coding for rat hepatic 6-phosphogluconate dehydrogenase has been isolated and used to measure changes in specific mRNA levels during dietary and hormonal regulation of this enzyme. Hepatic mRNA was fractionated by sucrose gradient centrifugation to enrich for 6-phosphogluconate dehydrogenase mRNA sequences. A cDNA library was prepared from the fraction with maximal activity and then screened by differential colony hybridization using probes synthesized either from 6-phosphogluconate dehydrogenase mRNA enriched by polysome immunoadsorption or from unenriched hepatic mRNA. A single colony giving an appropriate differential signal was confirmed to contain sequences encoding 6-phosphogluconate dehydrogenase by specific immunoprecipitation of hybrid-selected translational products. 6-Phosphogluconate dehydrogenase mRNA contains about 2400 bases. The cloned cDNA comprises about 880 bases, or 35% of the mRNA. Southern analysis of restriction endonuclease digests of genomic DNA suggests that the major 6-phosphogluconate dehydrogenase gene is probably present in a single copy in the rat genome. Feeding a fat-free, high carbohydrate diet and administration of thyroid hormone increased the concentration of hybridizable 6-phosphogluconate dehydrogenase mRNA in liver. Thus, both dietary and hormonal regulation of 6-phosphogluconate dehydrogenase synthesis occurs at a pretranslational level.
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PMID:Use of a cloned cDNA sequence to measure changes in 6-phosphogluconate dehydrogenase mRNA levels caused by thyroid hormone and dietary carbohydrate. 630 12

A large body of circumstantial evidence indicates that receptors located in nuclei of T3 responsive tissues represent a site of initiation of thyroid hormone action at the cellular level. Partial characterization of T3 receptors indicates that these proteins are monomeric structures in nuclei and are chromatin-associated non-histone proteins. Treatment of rat liver nuclei with either pancreatic DNase I or micrococcal nuclease releases T3 receptors from nuclei in two forms: a predominant (95 400 Mr; 5.5-6.0S) and a minor (265 000-365 000 Mr; 12.5S) nucleoprotein complex. Similar structures are excised from rat kidney, brain, and heart nuclei and from GH1 pituitary cell nuclei by micrococcal nuclease digestion. These endonuclease-excised receptor-containing complexes are significantly larger than the salt-extracted receptor (50 000 Mr; 3.5S). The presence of DNA and other non-receptor proteins in these structures indicates that T3 receptors probably function within multimeric complexes in vivo. Although T3 receptors appear to be associated with DNA between nucleosomes, i.e. linker DNA, it is not entirely clear whether all or only a fraction of T3 receptors interact with nucleosomal components. The 12.5S receptor-containing nucleoprotein complex may represent T3 receptors in association with linker DNA and nucleosomal components. T3 receptors do not appear to be uniformly distributed to all chromatin fractions, but are associated with structures having characteristics of transcriptionally active chromatin. They are found in a region of chromatin which is enriched in RNA polymerase activity, rapidly labeled RNA and non-histone proteins, and depleted of histone Hl. This region is also highly sensitive to both micrococcal nuclease and pancreatic DNase I digestion. The association of receptors with transcriptionally active chromatin, however, must be considered provisional until additional details of the precise receptor-chromatin interaction have been established. The recent demonstration of a 20-fold increase in a specific hepatic mRNA four hours following administration of T3 to hypothyroid rats indicates that thyroid hormone potentially has very rapid effects on hepatic gene expression. However, significant changes in nuclear protein phosphorylation, nuclear protein composition, and chromatin structure have not been detected within this four-hour period. Thus, effects of T3 on hepatic gene expression are brought about by local and presumably subtle changes in nuclear function.
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PMID:Association of thyroid hormone receptors with chromatin. 631 18

Rat liver nuclei were incubated with either thyroid hormone or angiotensin (AII) at varying concentrations or with buffer (control) prior to digestion with micrococcal nuclease. Concentrations of hormones greater than 10(-10)M were effective in increasing the solubilization of chromatin with physiological levels (10(-9)M) of AII showing an approximate 2.4 fold increase over control. Nuclei were also isolated from animals treated in-vivo with either AII or buffer (control) and chromatin solubility was increased in the AII treated nuclei even prior to the addition of exogenous nuclease, presumably from the action of endogenous nucleases. The data suggest that hormone-induced increases in solubility are a reflection of structural changes in chromatin which enhance the accessibility of DNA to endonuclease attack.
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PMID:Nuclear-hormone mediated changes in chromatin solubility. 683 24

The DNA mismatch repair (MMR) is a specialized system, highly conserved throughout evolution, involved in the maintenance of genomic integrity. To identify novel human genes that may function in MMR, we employed the yeast interaction trap. Using the MMR protein MLH1 as bait, we cloned MED1. The MED1 protein forms a complex with MLH1, binds to methyl-CpG-containing DNA, has homology to bacterial DNA repair glycosylases/lyases, and displays endonuclease activity. Transfection of a MED1 mutant lacking the methyl-CpG-binding domain (MBD) is associated with microsatellite instability (MSI). These findings suggest that MED1 is a novel human DNA repair protein that may be involved in MMR and, as such, may be a candidate eukaryotic homologue of the bacterial MMR endonuclease, MutH. In addition, these results suggest that cytosine methylation may play a role in human DNA repair.
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PMID:MED1, a novel human methyl-CpG-binding endonuclease, interacts with DNA mismatch repair protein MLH1. 1009 47

In the present study, we report a Thai female with a de novo mutation in thyroid hormone receptor-beta (TRbeta) gene causing resistance to thyroid hormone (RTH). The patient was a 19 year-old woman who presented with goiter for 1 year. Except for tachycardia she had no signs of thyrotoxicosis. Previously she was treated with propylthiouracil based on the diagnosis of thyrotoxicosis for 9 months and her goiter became more enlarged. The patient was the only child of the family. Her parents were alive and healthy, and did not have goiter or any other thyroid diseases. Physical examination revealed no sign of thyrotoxicosis. Her thyroid gland was diffusely enlarged with an estimated weight of 100 gm. Laboratory determinations revealed elevated free T4, T3 and nonsuppressed TSH levels. Exon 9 of the TRbeta gene was amplified by PCR and the DNA sequence was determined by dye terminator cycle sequencing. Heterozygous point mutation in which T was replaced by C was detected at position 1274 (TTG to TCG) corresponding to a leucine to serine substitution at codon 330. No mutation was found in the parents indicating that the mutation was de novo. The nucleotide change created a restriction site for Taq 1 restriction endonuclease and the mutation was confirmed by restriction fragments length polymorphism. The same nucleotide change has been reported in a family with RTH.
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PMID:A de novo L330S point mutation in thyroid hormone receptor beta gene in a Thai female with resistance to thyroid hormone. 1072 59

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