[Baculovirus vectors for efficient gene delivery and expression in mammalian cells]

Baculovirus expression vectors are extensively used for the delivering foreign genes and expression of recombinant proteins in insect and mammalian cells. Modified baculoviruses containing mammalian promoter elements (BacMam viruses) for an efficient transient and stable transduction of diverse mammalian cells prove a high level of heterologous proteins' expression both in vitro and in vivo. Recombinant baculovirus vectors containing mammalian expression cassette with cytomegalovirus promoter, green or red fluorescent protein gene, polyadenylate signal SV40pA, and polylinker MCS were constructed for the delivery of genes encoding hepatitis C virus structural proteins into mammalian cells. In Hek293T and Huh7 cells formation of glycoprotein complexes and HCV-like particles was observed. A high efficiency of the baculovirus-mediated gene transfer and expression of the virus envelope proteins in mammalian cells was demonstrated with using fluorescence, flow cytometry and immunoblot techniques.

[Characterization of hepatitis C virus structural proteins and HCV-like particles produced in recombinant baculovirus infected insect cells]

Three proteins, namely: "core" protein C and glycoproteins E1 and E2, are main structural proteins forming a hepatitis C vius (HCV) virion. The virus structure and assembly, a role of the structural proteins in virion morphogenesis remain unknown because of the lack of an efficient culture system for HCV to be grown in vitro. Using recombinant baculoviruses expressing HCV structural protein genes in insect cells the specific structural proteins at the level of 25-35% relative to a common cell protein content, heterodimers of the glcoproteins, and HCV-like particles have been obtained. It has been demonstrated that recombinant proteins C, E1, and E2 go through the posttranslation modification, the glycoproteins form the non-covalent heterodimer, and HCV-like particles are located in endoplasmatic reticulum membrains of infected cells. An ability of the expressed proteins for forming E1E2 dimers and HCV-like particles was used for studying the role of E1 protein glcosylation upon expression and processing of the glycoproteins.

Letter from the Editors

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The Interaction between the RNA-Dependent RNA-Polymerase of the Hepatitis Virus and RNA Matrices

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[Transcription and its regulation in mammalian and human mitochondria]

In eukaryotic cells mitochondria are the primary source of ATP, which is generated by oxidative phosphorylation. In humans and mammals these organelles contain their own maternally-inherited genome. Defects in mitochondrial gene expression result in a number of human diseases and contribute to aging. Transcription of mitochondrial genes is carried out by unique transcription machinery comprised of a single subunit bacteriophage T7-like mitochondrial RNA polymerase, together with several nuclear-encoded transcription factors. Mitochondrial transcription (and as a consequence oxidative phosphorylation) may be regulated by transcription initiation and termination factors, and by changes in ATP levels in response to alterations of the cell's metabolic demands. Recent data suggest that transcription in mitochondria is also coordinated with other crucial processes such as DNA replication and translation, indicating the importance of studies of molecular mechanisms of mitochondrial gene expression in these organelles.

Hepatitis C virus helicase/NTPase: an efficient expression system and new inhibitors

A method has been developed for obtaining a full-length protein NS3 of hepatitis C virus with the yield of 6.5 mg/liter of cell culture, and conditions for measuring its NTPase and helicase activities have been optimized. The helicase reaction can proceed in two modes depending on the enzyme and substrate concentration ratio: it can be non-catalytic in the case of enzyme excess and catalytic in the case of tenfold substrate excess. In the latter case, helicase activity is coupled with NTPase and is stimulated by ATP. A number of NTP and inorganic pyrophosphate analogs were studied as substrates and/or inhibitors of NS3 NTPase activity, and it was found that the structure of nucleic base and ribose fragment of NTP molecule has a slight effect on its inhibitory (substrate) properties. Among the nucleotide derivatives, the most efficient inhibitor of NTPase activity is 2 -deoxythymidine 5 -phosphoryl-beta,gamma-hypophosphate, and among pyrophosphate analogs imidodiphosphate exhibited maximal inhibitory activity. These compounds were studied as inhibitors of the helicase reaction, and it was shown that imidodiphosphate efficiently inhibited the ATP-dependent helicase reaction and had almost no effect on the ATP-independent duplex unwinding. However, the inhibitory effect of 2 -deoxythymidine 5 -phosphoryl-beta,gamma-hypophosphate was insignificant in both cases, which is due to the possibility of helicase activation by this ATP analog.

New non-nucleoside inhibitors of hepatitis C virus RNA-dependent RNA polymerase

Recombinant RNA-dependent RNA polymerase of hepatitis C virus was purified using a bacterial expression system (Escherichia coli). The system for enzyme activity detection was optimized. The maximum activity was achieved when the reaction was carried out at 30 degrees C in the presence of 3 mM Mg2+ or 0.75 mM Mn2+. Among alpha- and beta-pyrogallaldehydes, effective inhibitors were found. It was shown that they acted at the primer elongation stage, and their binding to the protein is reversible.

[Purification and site-directed mutagenesis of DNA methyltransferase SssI]

Prokaryotic DNA methyltransferase SssI (M.SssI) methylates C5 position of cytosine residue in CpG sequences. To obtain functionally active M.SssI and its mutants as His6-tagged proteins, bacterial strains have been produced. To test a possible role of Ser300 in recognition of CpG site by this enzyme, M.SssI mutants containing Ser300 replacements with Gly or Pro have been obtained. These replacements have practically no effect on DNA binding and methylation by M.SssI except small disturbance of DNA binding affinity in the case of S300P mutant. It indicates that there are no interactions of both the side chain and, probably, the main chain of Ser300 with DNA. A replacement of highly conserved Va1188 residue with Ala has been performed. Vall88 may participate in the stabilization of the flipped target cytosine during reaction. The replacement results in a 5-fold decrease of dissociation constant of the enzyme-substrate complex and a 2-fold decrease of initial velocity of DNA methylation. Though there are no noticeable differences in the functioning of the mutant in comparison with the wild-type enzyme, the formation of contact between Val 188 and cytosine could not be excluded. In the case of V 188A mutant the contact may be probably formed between Ala and cytosine residue.

Hepatitis C virus RNA-dependent RNA polymerase: study on the inhibition mechanism by pyrogallol derivatives

Pyrogallol reversibly and noncompetitively inhibits the activity of the hepatitis C RNA-dependent RNA polymerase. Based on molecular modeling of the inhibitor binding in the active site of the enzyme, the inhibition was suggested to be realized via chelation of two magnesium cations involved in the catalysis at the stage of the phosphoryl residue transfer. The proposed model allowed us to purposefully synthesize new derivatives with higher inhibitory capacity.

Interaction of HIV-1 reverse transcriptase with modified oligonucleotide primers containing 2'-O-beta-D-ribofuranosyladenosine

Modified synthetic oligodeoxyribonucleotides containing 2'-O-beta-D-ribofuranosyladenosine were used as primers in the RNA-dependent DNA synthesis catalyzed by HIV-1 reverse transcriptase. The degree of elongation of the primers depends on the position of the additional ribose unit, its presence in the specific position of the primer (-4) (and only in it) completely preventing elongation. Computer-modeled binding of the modified primers to the active site of reverse transcriptase demonstrated that steric hindrances arising from the interaction of the additional ribose residue with the reverse transcriptase region 262-270 interacting with the minor groove of the DNA substrate prevents elongation in the above mentioned case.

[Photoaffinity modification of bacteriophage T7 DNA-dependent RNA polymerase by the reaction product containing the azido derivative of UTP]

The possibility of using the 5-[3-(E)-(4-azido-2,3,5,6-tetrafluorobenzamido)-propenyl-1]-UTP (N3-TFBP-UTP) as the affinity modificator of bacteriophage T7 DNA-dependent RNA polymerase was demonstrated. The UTP derivative used was rather efficient substrate substituting UTP in the transcription reaction performed by the enzyme. The UV treatment of "stopped" reaction complex formed using three of four substrate ribonucleotides, allow to obtain the covalent binding between the enzyme and the reaction product of 9 nucleotides length. The isolation and the analysis of the obtained "nucleotide-peptide" showed that the sequence of modified peptide corresponded to the fragment Tyr802-Lys826, which belonged to the conservative motif C in the enzyme structure. His811 or Asp812 residues belonging to this sequence are most probable targets of the modification.

Oligonucleotides containing disaccharide nucleosides: synthesis, physicochemical, and substrate properties

The efficient synthesis of oligonucleotides containing 2'-O-beta-D-ribofuranosyl (and beta-D-ribopyranosyl)nucleosides, 2'-O-alpha-D-arabinofuranosyl (and alpha-L-arabinofuranosyl)nucleosides. 2'-O-beta-D-erythrofuranosylnucleosides, and 2'-O-(5'-amino-5-deoxy-beta-D-ribofuranosyl)nucleosides have been developed.

Structural-functional analysis of bacteriophage T7 RNA polymerase

This review summarizes our results of the structural and functional studies of bacteriophage T7 DNA-dependent RNA polymerase (T7 RNAP). Particular features of this enzyme (the single-subunit composition, relatively low molecular weight) make it the most convenient model for investigating the physicochemical aspects of transcription. The review discusses the main properties of T7 RNAP, interaction between the enzyme and promoter, principle stages of T7-transcription, and also the results of structural and functional studies by affinity modification and both random and site-directed mutagenesis techniques.

[Point contacts of T7 RNA polymerase in the promotor complex, as determined with phosphate-activated oligonucleotide derivatives]

The contacts between phosphate groups of promoter DNA an Lys or His of T7 RNA polmerase (Pol) in the Pol-promoter complex were studied with single- and double- stranded oligonucleotides, which corresponded to the T7 promoter consensus and contained activated phosphate groups at position +1, +2, or -14 relative to the transcription start. To obtain reactive groups, terminal phosphates were modified with N-oxybenzotriazole (HOBT), and internucleotide phosphates were repalced with a trisubstituted pyrophosphate (TSP). The resulting derivatives produced covalent complexes with T7 Pol. Covalent bonding involved His in the case of TSP at position +1 or HOBT at position +1 or -14, and Lys in the case of TSB at position -14.

An additional 2'-ribofuranose residue at a specific position of the DNA primer prevents Its elongation by HIV-1 reverse transcriptase

Oligodeoxynucleotides containing 2'-O-beta-D-ribofuranosyladenosine were prepared and used as modified primers in RNA-templated DNA synthesis catalyzed by HIV reverse transcriptase. It was shown that the additional 2'-ribofuranose residue in specific position of primer prevents its elongation.