Biomedical subjects

R Dikstein

Publications and source records attributed to R Dikstein.

4 recordsLinked to original sources

PubMed1992

c-abl has a sequence-specific enhancer binding activity.

The enhancers of several distinct viruses contain a common functional element, termed EP. This element binds ubiquitous cellular proteins and generates specific complexes in gel retardation analysis. Ultraviolet cross-linking and Southwestern analysis showed that a 140 kd polypeptide is the major EP DNA-binding protein. Using a combination of DNA binding and immunological techniques, we have identified the c-abl protein in a nuclear complex that binds to the EP element. abl was found to have both a specific and high affinity DNA binding activity. The ability to bind DNA is abolished in the mutant abl protein, p210bcr-abl, consistent with its cytoplasmic localization in chronic myelogenous leukemia.

Base Sequence↗

PubMed1990

Functional organization of the hepatitis B virus enhancer.

We have studied the functional constituents of the hepatitis B virus enhancer in a number of cell lines. The sequence of this enhancer, being embedded within an open reading frame of the virus, is in part evolutionarily frozen and therefore serves as a good model to investigate the fundamental enhancer elements. The hepatitis B virus enhancer contains three functionally important DNA sequence elements, EP, E, and NF-1a, each of which is bound by a distinct protein(s). The synergistic action of these elements accounts for all of the enhancer activity in a nonliver cell line and for most, but not all, of the activity in liver-derived cell lines. Multimers of the E but not of the EP element act as an autonomous enhancer. Conversely, a single element of either the E or the NF-1a element can act only when linked to the EP element. These results suggest that EP is a crucial enhancer element that acts only in interaction with a second enhancer element with intrinsic enhancer activity. Interestingly, a highly similar enhancer structure is found in a number of distinct viruses.

Animals↗

PubMed1990

Hierarchic and cooperative binding of the rat liver nuclear protein C/EBP at the hepatitis B virus enhancer.

We used the enhancer-binding protein C/EBP as a model to study the nature and the complexity of interaction of an enhancer-binding protein with its target DNA. We found that bacterially expressed C/EBP binds the hepatitis B virus enhancer at multiple sites in a hierarchic and cooperative manner. At low concentrations, only the E element is occupied, but at higher concentrations, additional sites are filled including a site that binds EP, a crucial enhancer-activating protein. This pattern of C/EBP binding may explain the concentration-dependent effect of C/EBP on enhancer activity.

Animals↗

PubMed1989

Liver-specific expression of hepatitis B virus is determined by the combined action of the core gene promoter and the enhancer.

The hepatitis B virus (HBV) enhancer and the core gene promoter regulate the expression of the core and polymerase genes, as well as of the 3.5-kilobase pregenomic RNA. RNA analysis and chloramphenicol acetyltransferase gene expression by plasmids carrying the HBV enhancer linked to the heterologous beta-globin or simian virus 40 early promoter demonstrated that the HBV enhancer is 3- to 20-fold preferentially expressed in human liver cells. Core gene promoter activity was mapped to a 100-base-pair fragment which was shown to be sufficient for accurate initiation of transcription. The partial tissue specificity of this promoter was demonstrated by transient transfection into various cell lines with a plasmid containing the core gene promoter linked to the heterologous simian virus 40 enhancer. When the HBV core gene promoter was examined under the control of the HBV enhancer, there was high tissue specificity in that activity could be observed only in differentiated human liver cells. These results suggest that the strict tissue specificity of HBV gene expression is determined by the combinatorial action of these two elements.

Animals↗