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Biomedical subjects

A B Vartapetian

Publications and source records attributed to A B Vartapetian.

At least 19 recordsLinked to original sources
PubMed2000

Early alteration of nucleocytoplasmic traffic induced by some RNA viruses.

A HeLa cell line expressing the green fluorescent protein fused to the SV40 T-antigen nuclear localization signal (EGFP-NLS) was established. Fluorescence in these cells was confined to the nuclei. After poliovirus infection, cytoplasmic fluorescence in a proportion of cells could be detected by 1 h postinfection (p.i.) and in virtually all of the fluorescent cells by 2 h p.i. The relocation could be prevented by cycloheximide but not by inhibition of poliovirus replication by guanidine. HCl. Nuclear exit of a protein composed of three copies of GFP fused to the NLS also occurred upon poliovirus infection. A similar redistribution of EGFP-NLS took place upon infection with coxsakievirus B3 and, to a lesser extent, with vesicular stomatitis virus. The EGFP-NLS efflux was not due to the loss of NLS. Thus, some positive-strand and negative-strand RNA viruses trigger a rapid nonspecific relocation of nuclear proteins.

Antigens, Polyomavirus Transforming↗
PubMed2000

Interaction of yeast importin alpha with the NLS of prothymosin alpha is insufficient to trigger nuclear uptake of cargos.

A proliferation-related human protein prothymosin alpha displays exclusively nuclear localization when produced in human and Saccharomyces cerevisiae cells, whereas its isolated bipartite NLS confers nuclear targeting of the GFP reporter in human but not in yeast cells. To test whether this observation is indicative of the existence of specific requirements for nuclear targeting of proteins in yeast, a set of prothymosin alpha deletion mutants was constructed. Subcellular localization of these mutants fused to GFP was determined in yeast and compared with their ability to bind yeast importin alpha (Srp1p) in vitro. The NLS of prothymosin alpha turned out to be both necessary and sufficient to provide protein recognition by importin alpha. However, the NLS-importin alpha interaction did not ensure nuclear targeting of prothymosin alpha derivatives. This defect could be complemented by adding distinct prothymosin alpha sequences to the NLS-containing import substrate, possibly by providing binding site(s) for additional components of the yeast nuclear import machinery.

Antigens, Viral, Tumor↗
PubMed2000

Prothymosin alpha fragmentation in apoptosis.

We observed fragmentation of an essential proliferation-related human nuclear protein prothymosin alpha in the course of apoptosis induced by various stimuli. Prothymosin alpha cleavage occurred at the DDVD(99) motif. In vitro, prothymosin alpha could be cleaved at D(99) by caspase-3 and -7. Caspase hydrolysis disrupted the nuclear localization signal of prothymosin alpha and abrogated the ability of the truncated protein to accumulate inside the nucleus. Prothymosin alpha fragmentation may therefore be proposed to disable intranuclear proliferation-related function of prothymosin alpha in two ways: by cleaving off a short peptide containing important determinants, and by preventing active nuclear uptake of the truncated protein.

Apoptosis↗
PubMed2000

Divalent metal cation binding properties of human prothymosin alpha.

The divalent cation binding properties of human prothymosin alpha, an abundant nuclear protein involved in cell proliferation, were evaluated. By using prothymosin alpha retardation on a weak cation chelating resin charged with various divalent cations, specific binding of Zn2+ ions by prothymosin alpha was observed. This finding was further confirmed by the equilibrium dialysis analysis which demonstrated that, within the micromolar range of Zn2+ concentrations, prothymosin alpha could bind up to three zinc ions in the presence of 100 mM NaCl and up to 13 zinc ions in the absence of NaCl. Equilibrium dialysis analysis also revealed that prothymosin alpha could bind Ca2+, although the parameters of Ca2+ binding by prothymosin alpha were less pronounced than those of Zn2+ binding in terms of the number of metal ions bound, the KD values, and the resistance of the bound metal ions to 100 mM NaCl. The effects of Zn2+ and Ca2+ on the interaction of prothymosin alpha with its putative partners, Rev of HIV type 1 and histone H1, were examined. We demonstrated that Rev binds prothymosin alpha, and that prothymosin alpha binding to Rev but not to histone H1 was significantly enhanced in the presence of zinc and calcium ions. Our data suggest that the modes of prothymosin alpha interaction with Rev and histone H1 are distinct and that the observed zinc and calcium-binding properties of prothymosin alpha might be functionally relevant.

Calcium↗
PubMed1999

Multiple tRNA attachment sites in prothymosin alpha.

A covalent complex formed by bacterial tRNAs and prothymosin alpha, an abundant acidic nuclear protein involved in proliferation of mammalian cells, upon production of the recombinant rat protein in Escherichia coli cells was studied. Several tRNA attachment sites were identified in the prothymosin alpha molecule using a combination of deletion analysis of prothymosin alpha and site-specific fragmentation of the protein moiety of the prothymosin alpha-tRNA complex. The electrophoretic mobilities of the tRNA-linked prothymosin alpha and its derivatives are consistent with one tRNA molecule attached to one prothymosin alpha molecule, thus suggesting that alternative tRNA linking to one of several available attachment sites occurs. The possible effect of tRNA attachment on the nuclear uptake of prothymosin alpha is discussed.

Amino Acid Sequence↗
PubMed1997

Mutational analysis of human prothymosin alpha reveals a bipartite nuclear localization signal.

Mutants of human prothymosin alpha with impaired ability to inhibit yeast Saccharomyces cerevisiae. cerevisiae cell growth were characterized. Two types of prothymosin alpha-inactivating mutations were observed. Mutations that belong to the first type compromised the nuclear entry of prothymosin alpha by affecting its nuclear localization signal. Analysis of subcellular distribution of GFP-prothymosin alpha fusions revealed a bipartite nuclear localization signal that is both necessary and sufficient for nuclear import of the protein in human cells. Mutations of the second type abrogated the inhibitory action of prothymosin alpha through an unknown mechanism, without influencing the nuclear import of the protein.

Amino Acid Sequence↗
PubMed1995

Overproduction in Escherichia coli, purification and properties of human prothymosin alpha.

A bacterial strain overproducing human prothymosin alpha was constructed based on the efficient T7 RNA polymerase transcription of human prothymosin alpha cDNA. The highest yield of the human prothymosin alpha, up to 30% of the total bacterial protein, was achieved with constructions containing 6-10 nucleotides between the Shine-Dalgarno sequence and initiation ATG codon. Unexpectedly, cells grown in the presence of inducer of T7 RNA polymerase synthesis produced substantially lower levels of prothymosin alpha than those grown in the absence of inducer. A simple procedure for prothymosin alpha isolation was elaborated, resulting in large amounts of electrophoretically pure and immunoactive protein.

Animals↗
PubMed1984

Encephalomyocarditis virus RNA synthesis in vitro is protein-primed.

A crude membrane-bound replication complex isolated from encephalomyocarditis virus-infected cells is able to initiate the synthesis of viral RNA. Both the formation of the primer, VPg-pU, and its utilization for the initiation of RNA chains take place in this system. A significant amount of the synthesized VPg-pU is found in the free form. The predominant product of the de novo initiation is represented by short phenol-soluble VPg oligonucleotide species, and only a small percentage of the latter appear to be elongated into longer RNA chains.

Animals↗
PubMed1983

The primary and secondary structure of the 5'-end region of encephalomyocarditis virus RNA. A novel approach to sequencing long RNA molecules.

The primary structure of a 149-nucleotide fragment of encephalomyocarditis (EMC) virus RNA from the 5'-terminus of the genome up to the poly(C) tract (S fragment) has been determined. For isolation of the S fragment, site-directed fragmentation of the viral RNA with RNase H and poly(dG) was employed. For sequencing the S fragment, a novel approach has been developed, which can be used for primary structure determination of long RNA molecules. A model of the secondary structure of the S fragment is proposed, according to which this region of RNA is highly structured. The role of complementary oligonucleotide stretches near both termini of the RNA molecule is discussed.

Base Sequence↗
PubMed1980

The structure of the covalent linkage between proteins and RNA in encephalomyocarditis virus.

Two protein, VPgA and VPgB, are covalently bound to the virion RNA of encephalomyocarditis (EMC) virus. Their molecular weightrs, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate are 10,000 and 8,000, respectively. A study of nucleotide-peptides isolated from VPg-RNA compound has shown that VPgA is bound to the 5'-terminal nucleotide of RNA by a phosphodiester bond. The 5'-terminal nucleotide of RNA is uridylic acid. It is the hydroxy group of the Tyr residue of VPgA that is involved in the formation of the linkage with RNA. VPgB-RNA seems to be similar to VPgA-RNA both in the structure of the RNA-protein linkage and localization of VPgB on RNA.

Alkaline Phosphatase↗
PubMedDate not supplied

[Novel functions of the well-known protein--prothymosin alpha is involved in protection of cells against apoptosis and oxidative stress].

Several novel functions of the well-known and intensively studied protein prothymosin alpha have recently been revealed. In addition to such traditional functions of this protein as immunomodulatory activity and stimulation of cellular proliferation, prothymosin alpha was shown to be involved in protection of cells against apoptosis and in regulation of expression of the oxidative stress-protective genes. Methods and approaches used for revelation of prothymosin alpha novel functions are described in this review.

Amino Acid Sequence↗
PubMedDate not supplied

[Polymerase chain reaction].

Principles of the polymerase chain reaction, its modifications and applications are discussed. Guidelines for performance of the polymerase chain reaction are briefly summarized.

DNA↗
PubMedDate not supplied

[Covalent bond between RNA and protein in encephalomyocarditis virus].

Deproteinized encephalomyocarditis [32P]RNA, after digestion with a mixture of RNases A, T1 and T2, yields mononucleotides and a labelled compound, which is positively charged at pH 3.5. This product can be digested with pronase and has a close electrophoretic mobility to a protein with a molecular weight of 7000-8000. Covalently bound nucleotide-peptides were isolated from this compound after treatment with RNases and pronase. It was shown that the 5'-terminal uridylic acid is covalently linked with peptides. The phosphodiester bond between uridylic acid and peptides is discussed.

Encephalomyocarditis virus↗
PubMedDate not supplied

[Genome-linked proteins in DNA and RNA viruses].

General principles of the organization of viral nucleic acid--protein covalent complexes are formulated. Participation of the genome-linked proteins in the initiation of viral nucleic acid replication is discussed.

DNA Viruses↗