Alteration of the Specificity of PstⅠ Restriction Endonuclease

The influence of factors on the subst rate-specificity of Pst Ⅰ restric tion endonuclease has been studied with the method of electrophoresis. The resu lts show that, the specificity of Pst Ⅰ almost can not be influenced by th e sin gle alteration of the concentration of Tris·HCl, Mg 2+ or Na+ in the rea ction s ystem, but it can be altered by the reduction of any two of them. The specificit y can not be altered by the single alteration of pH or the replacement of Mg 2+ w ith Mn 2+. The addition of glycerol or dimethylsulphoxide (DMSO) to the rea ction system results in the relaxation of the substrate-specificity of Pst Ⅰ , b ut dim ethylmethylformide, glycol and ethyl alcohol can not bring about the alteration of Pst Ⅰ specificity. Through the method of cloning and sequencing, the nuc leot ides of No.1 and 6 in the recognition sequence of Pst Ⅰ have changed (1C→A or 6 G→T). Used with the enzyme analysis of an artificially synthetic DNA segment co ntaining a special sequence, the nucleotides of No.1 and 6 have both changed (1C →A and 6G→T). The recognition sequence of Pst Ⅰ is speculated to be chan ged from CTGCA↓G to TGCA↓.

Restriction endonucleases digesting DNA in PCR buffer

Six commonly used restriction endonucleases (REs) (Acc I, Ban II, EcoR I, Hind III, Sac I, Sca I) were tested for their ability to directly digest DNA completely in the Polymerase Chain Reaction (PCR) buffers. The results showed that: with the requirement for addi- tional magnesium supplemented as activator, REs, except EcoR I appeared star activity, completely digested unmethylated lambda DNA af- ter overnight incubation in PCR buffer and functioned as equally well as in recommended Restriction Enzyme Buffer provided with each enzyme; all REs tested completely digested PCR products in PCR buffer, it implied digestion of PCR products may often be performed di- rectly in the PCR tube without the requirement for any precipitation or purification steps; and the concentration of MgCl2 from 2.5 mmol·L-1 to 10 mmol·L-1 did not significantly affect activity of REs in PCR buffer. This simplified method for RE digestion of PCR prod- ucts could have applications in restriction fragment length polymorphism (RFLP) analysis and single-stranded conformational polymor- phism (SSCP) analysis of large PCR products. However, usage of this procedure for cloning applications needs further data.

Polymorphism in Mitochondrial DNA of Six Fowl Breeds Revealed by Restriction Endonuclease

The patterns of cleavage of mtDNA by restriction endonucleases was analysed for six fowl breeds and of. Hyline White, Hyline Brown, ISA Brown, Hisex Brown, Lohmann White, Abor Acres and mtDNA polymorphisms were detected in the restriction patterns with the following eight enzymes, Ava Ⅰ, Ava Ⅱ, EcoR Ⅰ, Hind Ⅲ, Bam HI, Pvu Ⅱ, Pst Ⅰ, Hinc Ⅱ. The restriction cleavage patterns were identical among these breeds. Hyline White, Hyline Brown, ISA Brown, Hisex Brown, Lohmann White—A type. The patterns of Abor Acres were B type. Based on their mtDNA restriction types, all the breeds were classified into two groups. Genetic distances among these groups were calculated in order to define their phylogenetic relationships. The relationship among five egg line breeds is close, while Abor Acres (Broiler fowl) is relatively far from them. The results suggest that the difference of mtDNA could result from the different origins. The polymorphic sites in mtDNA of Hyline White has been located on a restriction map.

Elimination of inter-domain interactions increases the cleavage fidelity of the restriction endonuclease Dralll

Dralll is a type liP restriction endonucleases （REases） that recognizes and creates a double strand break within the gapped palindromic sequence CACTNNN^GTG of double-stranded DNA indicates nicking on the bottom strand; indicates nicking on the top strand）. However, wild type Dralll shows significant star activity. In this study, it was found that the prominent star site is CATSGTT;GTG, consisting of a star 5＇ half （CAT） and a canonical 3＇ half （GTG）. Dralll nicks the 3＇ canonical half site at a faster rate than the 5＇ star half site, in contrast to the similar rate with the canonical full site. The crystal structure of the Dralll protein was solved. It indicated, as supported by mutagenesis, that Dralll possesses a ~13a- metal HNH active site. The structure revealed extensive intra-molecular interactions between the N-terminal domain and the C-terminal domain containing the HNH active site. Disruptions of these interactions through site- directed mutagenesis drastically increased cleavage fidelity. The understanding of fidelity mechanisms will enable generation of high fidelity REases.

Kinetic Studies on the Irreversible Inhibition of Restriction Endonuclease Pst I by Site-Specific Inhibitors

The irreversible modifying effects onPst I of several inhibitors have been studied with the irreversible inhibition kinetic theory of single substrate reaction provided by Tsou, C. L. Pyridoxal phosphate (PLP), p-chloromercuribenzoic acid (PCMB), diisopropyl fluorophosphate (DEP), 2,3-diacetyl (DAC) and N-ethyl-5-phenylisoxazoliun-3′-sulfonate (woodward's reagent K, WRK) modify the lysine, cysine, serteine, arginine and carboxyl groups of the protein molecule respectively. These five inhibitors have been found to inhibit both the prime activity and star activity ofPst I. Used with the irreversible inhibition theory, the apparent inhibition rate constant,A and the microcosmic inhibition rate constants,k +0 andk′ +0 of every inhibitor were calculated. We also found that their inhibition effects belong to the noncompetitive irreversible inhibition. Results show that among the groups to be modified, some have nothing to do with the combination with the substrate, and some may have, but any of them isn't the only factor involved in the specific binding. Despite all this, they may take part in the catalysis of enzyme or have important effects on maintaining the active structure of enzyme molecules. Furthermore, serine and arginine residues are related to the alteration ofPst I conformation and then influence the ability ofPst I recognizing and incising DNA specifically.

Human DNA contains sequences homologous to the 5'-non-coding region of hepatitis C virus: characterization with restriction endonucleases reveals individual varieties

Objective To investigate a 272 base pair section of the 5' non coding region of genomic DNA from the peripheral blood monounuclear cells of healthy hepatitis virus C (HCV) negative human subjects (not patients) Mothods This sequence section bears interest because ① it harbors several potential methylation (Cp rich) sites, and ② it represents the largest part of its internal ribosomal entry site A pre PCR digestion protocol was established making consistent use of four restriction endonucleases selected for certain features: SmaI, XmaCI, MspI, and HpaII are inhibited if methylation(s) are present at certain cytosines within their cutting sequences Results The suspected HCV specific sequence was found in the DNA of each subject tested The pre PCR digestion assay reveals individual differences in their pattern of methylation, which may be due to possible epigenetic phenomena Conclusions The results provide formal proof that these HCV specific sequences are contained in the genomic or extra chromosomal target DNA, and probably belong to a new class of endogenous sequences

INACTIVATION OF THE CDKN2/pl6 GENE INDUCED BY METHYLATION AT 5'-CpG ISLAND AND ITS RELATION TO LUNG CANCER

Objectives: To investigate the methylation status of the CDKN2/pl6 gene 5′-CpG island, and study the relationship between the CDKN2/pl6 gene inactivation by methylation and lung cancer. Methods: Genomic DNA extracted from the specimens of lung cancer and normal lung tissue was digested with methylation-sensitive endonucleases, and Southern blotting was used to analyze the methylation status of the CDKN2/pl6 gene in 89 cases of lung cancer and 10 cases of normal lung tissue. Results: In 89 cases of lung cancer studied, the CDKN2/pl6 gene was shown to be methylated in 21 cases with the total methylation rate of 23.6% (21/89), in which there were 15 cases (16.9%) methylated atSmaI sites, 12 cases (13.5%) atSmaI sites and 6 cases at bothSmaI andSacII sites. The methylation of the CDKN2/pl6 gene occurred in 17 among 42 of pl6 protein negative cases of lung cancer with a rate of 40.5% (17/42), and in 3 among 47 of pl6 protein positive cases with a rate of 6.4% (3/47). The CDKN2/pl6 gene was not methylated in 10 cases of normal lung tissue. Conclusion: The aberrant methylation of the CDKN2/pl6 gene 5′-CpG island is probably an important mechanism of the gene inactivation, it may be involved in the genesis and progress of lung cancer.