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Biomedical subjects

B G Beltchev

Publications and source records attributed to B G Beltchev.

9 recordsLinked to original sources
PubMed1990

Differences between some properties of acetylated and nonacetylated forms of HMG1 protein.

There are data suggesting that HMG1 protein may be involved in DNA replication. Recently we have found that only the acetylated form of the protein generates tetramers, stimulates the activity of DNA polymerase alpha (EC 2.7.7.7) (with activated DNA as a template) and forms a specific complex with it. This paper compares some properties of the acetylated and nonacetylated forms of HMG1 protein and shows that it is only the acetylated form which serves as a histone assembly factor, increases the melting temperature of poly d[(A-T)] and stimulates the activity of DNA polymerase alpha when histone H1-depleted chromatin is used as a template.

Acetylation↗
PubMed1988

Acetylated HMG1 protein interacts specifically with homologous DNA polymerase alpha in vitro.

The acetylated, deacetylated and nonacetylated forms of HMG1 proteins from Guerin ascites tumour cells and calf thymus were separated and their in vitro interactions with homologous and heterologous DNA polymerases were studied. It has been found that only the acetylated form of HMG1 proteins forms a specific complex with homologous DNA polymerase alpha and stimulates its activity in vitro. The acetylation therefore is necessary for their possible function in DNA replication. This finding represents an evidence for a relationship between the acetylation of HMG1 proteins and their biological role.

Acetylation↗
PubMed1987

Differences between HMG1 proteins isolated from normal and tumour cells.

The properties of the non-histone chromosomal high-mobility-group 1 (HMG1) proteins from rat liver and Guerin ascites tumour cells (GAT cells) were compared and showed the following differences: (1) five spots were missing in the peptide map of HMG1 from GAT cells in comparison with that of HMG1 from rat liver; (2) HMG1 from GAT cells was about 5-times more poly(ADP)-ribosylated; (3) HMG1 from GAT cells which was found acetylated in vivo and incorporated [14C]acetate in vitro, whereas no incorporation of the label was detected in HMG1 from rat liver; (4) HMG1 from GAT cells exhibited pronounced ability to form oligomers at physiological ionic strength, while HMG1 from rat liver was predominantly in monomeric form. This property of HMG1 from GAT cells was lost upon deacetylation.

Acetylation↗
PubMed1986

Protein HMG1 is different from a DNA helix unwinding protein in calf thymus.

A number of criteria were used--chromatography on columns with single-stranded and double-stranded DNA, electrophoresis, peptide analysis, immunological tests and thermal denaturation of DNA--to show that protein (high mobility group) HMG1 and an unwinding protein from calf thymus are two distinct, unrelated proteins. While both proteins are thought to be related to DNA replication this might involve different mechanisms of action.

Animals↗
PubMed1984

Involvement of protein HMG1 in DNA replication.

Antibodies against HMG1 inhibit the incorporation of [3H]thymidine in Ehrlich ascites cell nuclei. By the use of specific inhibitors it is shown that HMG1 is needed for the action of the replicative DNA polymerase and not for the reparative one. This is supported by the fact that the addition of exogenous HMG1 to the nuclei enhances the replication process.

Animals↗
PubMed1984

Isolation of high-mobility-group proteins HMG1 and HMG2 in non denaturing conditions and comparison of their properties with those of acid-extracted proteins.

We describe a method for isolation and purification of the chromosomal proteins HMG1 and HMG2 in non-denaturing conditions which overcomes the difficulties of the published methods concerning yield and purity. The method is based on salt extraction, selective precipitation with ammonium sulfate and DEAE-cellulose chromatography. All studied properties of these proteins (formation of protein tetramers, enhancement of micrococcal nuclease digestion of DNA and chromatin, and protection of 165-basepair DNA in chromatosome) differ significantly from the properties of HMG1 and 2 isolated under denaturing conditions.

Animals↗
PubMed1984

High mobility group proteins HMG1 and HMG2 do not decrease the melting temperature of DNA.

High mobility group proteins 1 and 2 isolated in non-denaturing conditions cannot decrease the temperature of denaturation of DNA. When they are isolated or treated with tricloroacetic acid a hyperchromic peak below the melting temperature of free DNA appears in agreement with previous data ( Javaherian et al. (1979) Nucl . Acids Res. 6, 3569-3580). We show that this is due to light scattering of aggregated protein at submelting temperatures and not to melting of DNA.

Animals↗