Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.26.4 (RNase H)
 2,751 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent interest in the use of adriamycin-DNA complex as an approach to improve the therapeutic effectiveness and to reduce toxicity of adriamycin for cancer chemotherapy requires an in-depth understanding of the physicochemical and biochemical properties of such complexes. The interactions of adriamycin with single-strand polydeoxyribonucleotides, double-strand DNA, and double-strand ribodeoxyribopolynucleotide hybrids were therfore investigated. Association constants (Kapp) of adriamycin and polynucleotides were obtained. These data showed that the inherent variable in such complex lies in the composition of the polynucleotides. Alternate deoxyguanylate (dG)-deoxycytidylate (dC) sequence binds 7-fold better than alternate deoxyadenylate (dA)-deoxythymidylate (dT) sequence. Comparative studies of the hydrolysis of DNA duplexes by deoxyribonucleases I and II with and without adriamycin were also carried out. The rate of hydrolysis decreased in the order poly(dA-dT) greater than calf thymus DNA greater than poly(dG-dC) greater than poly(dA)-poly(dT) greater than poly(dG)-poly(dC) for DNase I and poly(dA)-dT) greater than calf thymus DNA greater than poly(dG-dC) greater than poly(dA)-poly(dT) greater than poly(dG)-poly(dC) for DNase II. Intercalation of adriamycin to deoxyribopolynucleotide duplex resulted in inhibition of DNase II two to three times more than tat of DNase I. On the other hand, intercalation of adriamycin to homodeoxypolynucleotide duplex poly(dA)-poly(dT) and poly(dG)-poly(dC) enhanced the DNase I hydrolysis. If DNase I activity could be related to serum DNase and DNase II related to tumor lyososomal DNase as in the endocytosis mechanism proposed by Trouet et al. (Cancer Chemotherapy Rept., 59: 260, 1975), the best adriamycin carrier suggested by this investigation could be poly(dA)-poly(dT) and poly(dG-dC). It is also suggested in this study that adriamycin-RNA-DNA hybrid could be of interest as an antiviral agent by a similar release mechanism via RNase H, an enzyme associated with viral reverse transcriptase.
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PMID:Effect of deoxyribonuclease on adriamycin-polynucleotide complexes. 97 96

In this study we describe DNA-RNA complexes in matrix DNA of Friend cells. The presence of such unusual structures is confirmed by the following evidence. When a preparation of matrix DNA is electrophoresed in agarose an RNA component always migrates together with DNA. There should be a close interaction between DNA and RNA in such a preparation because the presence of the RNA component causes resistance of DNA to DNase I and Exo III. An intimate, hybrid-type association of part of the RNA component with DNA is indicated also by the fact that about 20% of this RNA is sensitive to RNase H. By specific inhibition of the RNA synthesis with alpha-amanitin and actinomycin D it was shown that the bulk of associated RNA is transcribed by RNA polymerase III. Hybridization experiments showed similarity between the DNA sequences isolated from the complexes and those from the base of dehistonized DNA loops obtained by high-salt extraction of nuclei. This observation suggests that the complexes might represent attachment sites of nuclear DNA to the matrix: possibly, the attachment is mediated via the RNA component. Experiments with induction of erythroid differentiation indicated that a profound reorganization of the nucleus, accompanying terminal differentiation, leads to a striking reduction in the number of complexes and thus in the number of attachment sites. This suggests that the complexes should function as transient attachment sites.
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PMID:DNA-RNA complexes that might represent transient attachment sites of nuclear DNA to the matrix. 169 80

The three-dimensional structure of RNase H from Escherichia coli was determined at 1.8 A resolution by X-ray crystallography. The enzyme was found to belong to the alpha + beta class of structures, consisting of two distinct domains. The structure implies a possible region interacting with a DNA-RNA hybrid. The Mg2(+)-binding site essential for activity is located near a cluster of four acidic amino acids--one glutamic and three aspartic acid residues. These residues are completely conserved in the homology alignment of sequences of RNase H and reverse transcriptases from retroviruses and retrovirus-like entities. The structural motif of beta strands around the Mg2(+)-binding site has similarities to that in DNase I.
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PMID:Three-dimensional structure of ribonuclease H from E. coli. 169 62

Oligodeoxynucleotides with different arrangements of methylphosphonate linkages were examined for nuclease sensitivity in vitro, stability in tissue culture, and ability to form RNase H-sensitive substrates with complementary RNA. After nuclease treatment, resistance was demonstrated by the ability to alter the electrophoretic mobility of a labeled complementary phosphodiester oligodeoxynucleotide. Both 5'- and 3'-exonuclease activities were retarded by methylphosphonate linkages. Methylphosphonate-containing oligodeoxynucleotides with 1-5 adjacent phosphodiester linkages were tested as substrates for the endonucleases DNase I and DNase II. The results indicated that a span of three or fewer contiguous internal phosphodiester linkages led to the greatest resistance to endonuclease. However, in serum-supplemented culture medium half-lives of these oligodeoxynucleotides were independent of the number of contiguous phosphodiester linkages. Methylphosphonate-containing oligodeoxynucleotides were hybridized to RNA runoff transcripts and tested as substrates for RNase H. The results indicated that a span of three internal phosphodiester linkages in the oligodeoxynucleotide was necessary and sufficient to direct cleavage of the RNA in the duplex.
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PMID:Number and distribution of methylphosphonate linkages in oligodeoxynucleotides affect exo- and endonuclease sensitivity and ability to form RNase H substrates. 247 96

A double stranded RNA species has been detected in guanidine hydrochloride extracts of mitochondria from respiratory competent cells of Saccharomyces cerevisiae. This novel mitochondrial RNA, termed mtdsRNA, has been purified in a Cs2SO4 density gradient where it bands at a density of 1.58 g/ml. The mtdsRNA runs as a single slow moving band on agarose gels. Its double stranded RNA character was evidenced by its sensitivity to digestion by RNase III, but not by RNase H, or DNase I. Moreover the mtdsRNA hybridized to each separated strand of a petite mtDNA. It is concluded that mtdsRNA contains long transcripts derived from most regions of yeast mtDNA, because 1) its weight-average length as determined by electron microscopy was 4.5 micrometer (about 14 kb, or 20% of the wild type mtDNA genome), and 2) it hybridized to each of a series of eight petite mtDNA probes carrying sequences derived from widely different segments of mtDNA. It is proposed that prolonged transcription of both strands of yeast mtDNA can occur and that mtdsRNA arises from hybridization of these long complementary transcripts.
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PMID:A novel species of double stranded RNA in mitochondria of Saccharomyces cerevisiae. 627 33

"BcgI cassette" mutagenesis was used to prepare variants of p66 human immunodeficiency virus (HIV)-1 reverse transcriptase with amino acid substitutions between residues Glu224 and Trp229. Mutant polypeptides were reconstituted in vitro with wild type p51 to generate the "selectively mutated" heterodimer series p66(224A)/p51-p66(229A)/p51. Purified enzymes were characterized with respect to dimerization, DNA polymerase, RNase H, and tRNA(Lys-3) binding. The combined analyses indicate that while alteration of p66 residues Glu224-Leu228 has minimal consequences, the DNA polymerase activities of mutant p66(229A)/p51 are impaired. DNase I footprinting illustrates that this mutant does not form a stable replication complex with a model template-primer. In vivo studies indicate that the equivalent mutation eliminates viral infectivity, suggesting a contribution of Trp229 toward architecture of the p66 primer grip.
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PMID:Mutating the "primer grip" of p66 HIV-1 reverse transcriptase implicates tryptophan-229 in template-primer utilization. 752 8

Replication complexes containing wild-type and RNase H-deficient p66/p51 human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) were analyzed by DNase I and S1 footprinting. While crystallography and chemical footprinting data demonstrate that 15-18 bases of primer and template occupy the DNA polymerase and RNase H active centers, enzymatic footprinting suggests that a larger portion of substrate is encompassed by the replicating enzyme. Independent of the position of DNA synthesis arrest, template nucleotides +7 to -23 and primer nucleotides -1 to -25 are nuclease resistant. On both DNA strands, position -20 remains accessible to DNase I cleavage, suggestive of an alteration in nucleic acid structure between exiting the RNase H catalytic center and leaving the C-terminal p66 domain. A model of HIV-1 RT containing an extended single-stranded template and duplex region was constructed on the basis of the structure of an RT/DNA complex. Mapping of footprint data onto this model shows consistency between biochemical and structural data, implicating a contribution from domains proximal to the catalytic centers.
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PMID:An expanded model of replicating human immunodeficiency virus reverse transcriptase. 753 89

In order to investigate the modes of DNA synthesis supported by the 66 and 51 kDa subunits of equine infectious anemia virus reverse transcriptase (EIAV RT), recombinant p66 polypeptides containing a modified ribonuclease H (RNase H) domain were purified and evaluated. Defined heteropolymeric template-primer combinations and high-resolution gel electrophoresis provided a qualitative evaluation of DNA polymerase and RNase H activities, while DNase I footprinting revealed features of replication complexes containing the truncated enzymes. Removal of alpha-helix E' and the conserved beta 5'-alphaE' "His-loop" in p66delta20 RT uncouples the RNase H activities, alters affinity for template-primer and dictates how the replicating enzyme responds to secondary structure on both DNA and RNA templates. Despite these alterations, DNase I footprinting shows no major difference in the overall structure of DNA-directed DNA synthesis complexes. In contrast, removing 47 C-terminal residues, which includes alpha-helix D', beta-strand 5' and alpha-Helix E', yields an enzyme with distributive DNA polymerase properties closely resembling the purified p51 subunit.
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PMID:Involvement of C-terminal structural elements of equine infectious anemia virus reverse transcriptase in DNA polymerase and ribonuclease H activities. 864 20

The biochemical and physicochemical properties of DNA oligomers containing phosphorodithioate linkages in various configurations were evaluated. Duplex stability studies, which were carried out by thermal denaturation analysis with complementary unmodified DNA, indicated a highly cooperative process similar to completely unmodified duplexes. Oligomers containing phosphorodithioate linkages were found to have reduced melting temperatures relative to unmodified duplexes, with the degree of Tm depression paralleling the percent phosphorodithioate composition of the oligomer. Relative to activation of RNase H, DNA oligomers containing up to 50% phosphorodithioate linkages were able to direct RNase H degradation with the same efficiency as unmodified DNA while those containing from 50 to 100% acted with somewhat reduced efficiency. At limiting concentrations, an oligomer containing alternating phosphorodithioate and phosphate linkages was able to direct RNase H degradation of the target RNA in an extended incubation, while an unmodified oligomer did not. The nuclease resistance of phosphorodithioate-containing oligomers was evaluated in HeLa cell nuclear and cytoplasmic extracts, in human serum, and with nucleases S1 and DNase I. Oligomers containing alternating phosphorodithioate and phosphate were highly resistant to degradation in all systems. However, oligomers having more than one unmodified linkage separating phosphorodithioates were degraded rapidly by DNase I, while demonstrating stability to degradation in all other systems tested. These results indicate that phosphorodithioate-containing DNA oligomers are highly nuclease-resistant, are able to form stable duplexes with complementary nucleic acid sequences, and efficiently direct RNase H degradation of target RNA.
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PMID:Biochemical and physicochemical properties of phosphorodithioate DNA. 867 36

Hormone-sensitive lipase (HSL) catalyses the rate-limiting step of adipose tissue lipolysis. The human HSL gene is composed of nine exons encoding the adipocyte form and a testis-specific coding exon. Northern blot analyses showed that human adipocytes express a 2.8 kb HSL mRNA, suggesting the presence of a short (20-150 bp) 5' untranslated region (5'-UTR). A single 5'-UTR of approx. 70 nt was detected in RNase H mapping experiments. Two 5'-UTRs of 70 and 170 nt respectively were obtained by rapid amplification of cDNA ends and cDNA library screenings. RNase protection experiments, with probes derived from the two products, showed that human adipocyte HSL mRNA contains only the 70 nt product. Primer extension analysis mapped the transcriptional start site 74 nt upstream of the start codon. In HT29, a human cell line expressing HSL, the presence of the short or the long 5'-UTR is mutually exclusive. The short and long 5'-UTR exons were located 1.5 and approx. 13 kb respectively upstream of the first coding exon. Various portions of the 5'-flanking region upstream of the short product exon were linked to the luciferase gene and transfected into cells that express HSL (HT29 cells and rat adipocytes) and do not express HSL (HeLa cells). High luciferase activity was found for constructs containing the sequence between nt -2400 and -86, but not for shorter constructs. An analysis of 14 kb of genomic sequence revealed the presence of five DNase I hypersensitive sites associated with active gene transcription. Three of the sites are located in the vicinity of the transcriptional start site and could be linked to the minimal promoter activity. Two of the sites are located downstream of the exon containing the start codon, suggesting the presence of intronic regulatory elements.
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PMID:Characterization of the promoter of human adipocyte hormone-sensitive lipase. 937 1


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