Group Ⅱ introns are self-splicing ribozymes, which insert directly into target sites in DNA with high frequency through "retrohoming". They specifically and efficiently recognize and splice DNA target sites, endowing themselves with great potential in genetic engineering. This paper reviewed the gene targeting principle of group Ⅱ introns and the application in microbial genetic modification, and then analyzed the limitations of them in multi-functional gene editing and eukaryotes based on the "retrohoming" characteristics and the dependence on high Mg²⁺ concentration. Finally, we dissected the potential of group Ⅱ introns in the development of novel gene editing tools based on our previous research outcome and the structural characteristics of the introns, hoping to provide a reference for the application of group Ⅱ introns in biotechnology.
DNA ; Eukaryota ; Gene Targeting ; Introns/genetics* ; RNA, Catalytic/genetics*

BACKGROUNDTo express in vitro the bovine enterokinase catalytic subunit (EKL) protein, which could be used in the future for the cleavage and purification of fusion proteins.

METHODSBovine enterokinase catalytic subunit cDNA was obtained by RT-PCR from duodenal mucosa of a bovine obtained at wholesale market, and then cloned into a pUCmT cloning vector and sequenced. The desired gene fragment was inserted into a pET39b expression plasmid and the recombinant vector pET39b-EKL was transformed into E. coli BL21 (DE3). Protein expression was induced using IPTG. The recombinant DsbA-EKL was purified with His.Tag affinity chromatography, and it bioactivity was analyzed.

RESULTSCompared with the sequence deposited in GenBank, the sequence of the EKL gene cloned in the present study is correct. It was also confirmed that the nucleotide sequence of expression plasmid pET39b-EKL was correct at the conjunction site between the recombinant DNA 5' terminal multi-cloning site and the recombinant fragment. SDS-PAGE analysis indicated that the target product was about 65 kDa and represented 28% of total cell protein. Purified recombinant protein was obtained by metal chelating chromatography using Ni-IDA resin. After desalting and changing the buffer, the crude kinase was incubated at 21 degrees C overnight and shown to have a high autocatalytic cleavage activity.

CONCLUSIONSThe EKL gene from Chinese bovine has been cloned successfully and expressed. This investigation has layed the foundation for future enterokinase activity research and for further large-scale application of expression products.

Animals ; Catalytic Domain ; genetics ; Cattle ; Cloning, Organism ; DNA, Complementary ; Enteropeptidase ; analysis ; genetics ; Recombinant Proteins

DNA, Catalytic ; genetics ; Gene Expression ; Genetic Therapy ; Hep G2 Cells ; Hepacivirus ; genetics ; Humans ; Ribosomes ; genetics ; Transfection

OBJECTIVETo study the cleavage activity of specific deoxyribozyme to hepatitis C virus in vitro.

METHODSThree deoxyribozymes were designed to cleave at sites 157, 168, 173 in HCV 5'-noncoding region with the active region of 5'-GGCTAGCTACAACGA-3' respectively. Plasmid pCMV/T7-NCRC -Delta Luc was completely linearized with restriction endonuclease Xba I. HCV RNA5'-NCRC was transcribed in vitro from the linearized products and radiolabelled with [alpha-32P] UTP. Under the conditions of 37 degrees C, pH7.5, Mg2+ 10 mmol/L, the three deoxyribozymes were mixed with substrate RNA individually for 120 minutes and then the reactions were terminated. The cleavaged products were separated with 8% denaturated polyacrylamide gel electrophoresis and displayed by autoradiography. DRz3 was mixed with the substrate RNA at different Mg2+ concentrations. The cleavage efficiency was analyzed with a gel document action analyzing systems.

RESULTSUnder the adopted conditions the three deoxyribozymes efficiently cleaved to the target RNA in vitro and the cleavage activity of DRz3 was increased with the increase of Mg2+ concentration.

CONCLUSIONThe designed deoxyribozymes can cleave 5'-NCR mRNA of HCV efficiently in vitro and it is dose-respondent to Mg2+ concentration.

DNA, Catalytic ; genetics ; DNA, Single-Stranded ; genetics ; Genetic Therapy ; Hepacivirus ; genetics ; Hepatitis C ; therapy ; Humans ; RNA, Messenger ; genetics

PURPOSE: DNA-dependent protein kinase (DNA-PK) is a serine/threonine kinase consisting of a 470 kDa catalytic subunit (DNA-PKcs) and a heterodimeric regulatory complex, called Ku, which is composed of 70 kDa (Ku 70) and 86 kDa (Ku 80) proteins. The DNA-PK has been shown to play a pivotal role in rejoining DNA double-strand-breaks (dsb) in mammalian cells. The purpose of this study is to examine the relationship between the level of Ku expression and radiation sensitivity. METHODS AND MATERIALS: Nine head and neck, cancer cell lines showed various intrinsic radiation sensitivities. Among the nine, AMC-HN-3 cell was the most sensitive for X-ray irradiation and AMC-HN-9 cell was the most resistance. The most sensitive and resistant cell lines were selected and the test sensitivity of radiation and expression of Ku were measured. Radiation sensitivity was obtained by colony forming assay and Ku protein expression using Western blot analysis. RESULTS: Ku80 increased expression by radiation, wheres Ku70 did not. Overexpression of Ku80 protein increased radiation resistance in AMC-HN9 cell line. There was a correlation between Ku80 expression and radiation resistance. Ku80 was shown to play an important role in radiation damage response. CONCLUSION: Induction of Ku80 expression had an important role in DNA damage repair by radiation. Ku80 expression may be an effective predictive assay of radiosensitivity on head and neck cancer.
Blotting, Western ; Catalytic Domain ; Cell Line* ; DNA ; DNA Damage ; DNA-Activated Protein Kinase ; Head and Neck Neoplasms* ; Head* ; Neck ; Phosphotransferases ; Radiation Tolerance*

Echinostoma cinetorchis is an oriental intestinal fluke causing significant pathological damage to the small intestine. The aim of this study was to determine a full-length cDNA sequence of E. cinetorchis endoribonuclease (RNase H; EcRNH) and to elucidate its molecular biological characters. EcRNH consisted of 308 amino acids and showed low similarity to endoribonucleases of other parasites (<40%). EcRNH had an active site centered on a putative DDEED motif instead of DEDD conserved in other species. A recombinant EcRNH produced as a soluble form in Escherichia coli showed enzymatic activity to cleave the 3′-O-P bond of RNA in a DNA-RNA duplex, producing 3′-hydroxyl and 5′-phosphate. These findings may contribute to develop antisense oligonucleotides which could damage echinostomes and other flukes.
Amino Acids ; Catalytic Domain ; DNA, Complementary ; Echinostoma* ; Endoribonucleases ; Escherichia coli ; Intestine, Small ; Oligonucleotides, Antisense ; Parasites ; Ribonuclease H* ; Ribonucleases* ; RNA ; Trematoda

OBJECTIVETo analyze the cleavage activity of two deoxyribozymes targeting at hepatitis C virus (HCV) RNA in vitro and evaluate their prospects of antiviral therapy.

METHODSTwo specific sequences containing 5' ...A / U... 3' in HCV 5'-noncoding region and 5'-fragment of C region (5'-NCR-C) were selected as the target sites, and with the active region of 5'GGCTAGCTACAACGA3', two phosphorothioate deoxyribozymes (TDRz) named as TDRz-127 and TDRz1 were synthesized. HCV RNA 5'-NCR-C was transcribed in vitro from plasmid pHCV-neo which was completely linearized with restriction endonuclease Nar I, and its 5'-end phosphoric acid was deleted by calf intestinal alkaline phosphatase (CIP), then radiolabelled with T4 polynucleotide kinase and gamma-32P-ATP. Under the conditions such as pH 7.5 and a 10 mmol/L Mg2+ concentration, TDRz-127 and TDRz1 were separately (a 5 micromol/L final concentration) or combinedly (each 2.5 micromol/L) mixed with the substrate RNA (200 nmol/L). After denaturation and then renaturation, the reaction systems were incubated in 37 degrees C, and aliquots were removed to terminate the reaction at intended time points. The cleavage products were separated with 8% denaturated polyacrylamide gel electrophoresis and displayed by autoradiography. Finally, the optical density of each product band was measured with Gel Documentation-Analyzing Systems for calculating the percentages of cleaved HCV 5'-NCR-C.

RESULTSAfter reaction for 15, 30, 45, 60, 75 and 90 min under the adopted conditions, about 8.3%, 16.1%, 24.3%, 26.2%, 29.4% and 31.1% of HCV 5'-NCR-C was cleaved by TDRz-127 respectively; 7.4%, 13.0%, 15.6%, 18.7%, 19.4% and 20.3% by TDRz1; and 15.1%, 29.6%, 37.8%, 39.1%, 41.5%, 42.6% by combining the two TDRzs.

CONCLUSIONSCleavage percentage of both TDRz-127 and TDRz1 increases with the time, and the effect of combining the two TDRzs is better than that of anyone.

5' Untranslated Regions ; metabolism ; Base Sequence ; DNA, Catalytic ; genetics ; metabolism ; Hepacivirus ; enzymology ; genetics ; Humans ; Molecular Sequence Data ; RNA Processing, Post-Transcriptional ; RNA, Catalytic ; metabolism ; RNA, Viral ; metabolism ; mRNA Cleavage and Polyadenylation Factors ; genetics ; metabolism

PURPOSE: DNA-PKcs is one of the DNA repair genes. It was recently found that hyperplasia and dysplasia of the intestinal mucosa and the production of aberrant crypt foci were developed in DNA-PKcs-null mice, and this suggests a suppressive role for DNA-PKcs in tumorigenesis. MATERIALS AND METHODS: To investigate the possible relationship between the clinico-pathologic characteristics and the survival of gastric cancer patients, the expression status of DNA-PKcs was determined in 279 consecutive gastric cancers. Immunohistochemical analysis was performed to evaluate the expression levels of DNA-PKcs protein by using the tissue array method. RESULTS: Out of 279 consecutive gastric cancers, 63 cases (22.6%) showed the loss of DNA-PKcs expression. The loss of DNA-PKcs expression was significantly associated with advanced cancer (p <0.001), lymphatic invasion (p=0.001), lymph node metastasis (p=0.009), and advanced pTNM stage (p=0.009). Univariate survival analysis revealed that patients with the loss of DNA-PKcs expression had significantly poorer survival than those patients with intact DNA-PKcs expression (p=0.004). Moreover, the loss of DNA-PKcs expression was identified to correlate with a lower survival in the subgroup of stage I gastric cancer patients (p=0.037). CONCLUSION: The loss of DNA-PKcs expression was found in 23% of human gastric cancers and this was identified to significantly correlate with poor patient survival, especially for stage I gastric cancer patients.
Aberrant Crypt Foci ; Animals ; Carcinogenesis ; Catalytic Domain* ; DNA Repair ; DNA-Activated Protein Kinase* ; Humans ; Hyperplasia ; Immunohistochemistry ; Intestinal Mucosa ; Lymph Nodes ; Mice ; Neoplasm Metastasis ; Stomach Neoplasms* ; Survival Analysis

OBJECTIVETo investigate the cleavage activities of 10-23 DNA enzymes targeting at HBV C gene mRNA in vitro.

METHODS10-23 DNA enzymes named DrzBC-7, DrzBC-8 and DrzBC-9 specific to HBV C gene ORF A1816UG were designed and synthesized. HBV C gene mRNA was obtained by in vitro transcription method. Cleavage activities were observed in vitro. The influence of MgCl2 concentration on RNA cleaving activity was examined with DrzBC-9. Values of kinetic parameters including Km, Kcat and Kcat/Km were calculated accordingly.

RESULTTargeted substrate mRNA with the size of 300 nt was obtained by transcription in vitro. Under the certain cleavage conditions, DrzBC-7, DrzBC-8 and DrzBC-9 all efficiently cleaved target mRNA at specific sites in vitro. Cleavage products of 109 nt and 191 nt were obtained. No cleavage occurred without MgCl2. The most efficient cleavage was obtained at 150 mmol x L(-1) MgCl2. The efficiency of cleavage did not increase when the MgCl2 concentration was more than 200 mmol x L(-1). The kinetic parameters, Km, Kcat and Kcat/Km for DrzBC-9 were 1.4x10(-9) mol x L(-1), 1.6 min(-1) and 1.1x10(9) mol x L(-1) x min(-1), respectively.

CONCLUSION10-23 DNA enzymes targeting at HBV C gene mRNA possess the specific cleavage activities in vitro.

DNA, Catalytic ; metabolism ; DNA, Single-Stranded ; metabolism ; Hepatitis B virus ; enzymology ; genetics ; Open Reading Frames ; RNA, Messenger ; metabolism ; RNA, Viral ; genetics ; metabolism ; Transcription, Genetic

Integrase plays a critical role in the recombination of viral DNA into the host genome. Therefore, over the past decade, it has been a hot target of drug design in the fight against type 1 human immunodeficiency virus (HIV-1). Bovine immunodeficiency virus (BIV) integrase has the same function as HIV-1 integrase. We have determined crystal structures of the BIV integrase catalytic core domain (CCD) in two different crystal forms at a resolution of 2.45 Å and 2.2 Å, respectively. In crystal form I, BIV integrase CCD forms a back-to-back dimer, in which the two active sites are on opposite sides. This has also been seen in many of the CCD structures of HIV-1 integrase that were determined previously. However, in crystal form II, BIV integrase CCD forms a novel face-to-face dimer in which the two active sites are close to each other. Strikingly, the distance separating the two active sites is approximately 20 Å, a distance that perfectly matches a 5-base pair interval. Based on these data, we propose a model for the interaction of integrase with its target DNA, which is also supported by many published biochemical data. Our results provide important clues for designing new inhibitors against HIV-1.
Animals ; Catalytic Domain ; genetics ; Cattle ; DNA ; genetics ; DNA, Viral ; HIV-1 ; genetics ; metabolism ; Humans ; Immunodeficiency Virus, Bovine ; enzymology ; genetics ; Integrases ; chemistry ; genetics ; metabolism