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D Bohmann

Publications and source records attributed to D Bohmann.

44 records · Page 3Linked to original sources
PubMed1988

v-jun encodes a nuclear protein with enhancer binding properties of AP-1.

The jun oncogene of ASV17 is expressed as a 65 kd protein (p65gag-jun) that contains partial gag sequences at its amino terminus fused to jun sequences that make up the carboxy terminal two-thirds of the molecule. As a first step toward evaluating potential functional differences between the activated oncogene, v-jun, and its cellular counterpart, c-jun, we have characterized the biochemical properties of the gag-jun product of ASV17. Immunofluorescence studies revealed that the v-jun protein is localized in the nucleus of CEF transfected with ASV17 DNA. DNAase I foot-printing analysis indicates that p65gag-jun synthesized in bacteria binds to enhancer elements in SV40 that are recognition sites for the human transcription factor AP-1. Analysis of point mutants confirmed that v-jun protein binds with DNA sequence specificity of the mammalian enhancer factor AP-1 and the yeast transcription factor GCN4. These findings suggest that activation of the jun oncogene may not exclusively be the result of alterations in the DNA binding properties of the normal cellular protein.

Adenovirus Early Proteins↗
PubMed1987

Human proto-oncogene c-jun encodes a DNA binding protein with structural and functional properties of transcription factor AP-1.

Nuclear oncogene products have the potential to induce alterations in gene regulation leading to the genesis of cancer. The biochemical mechanisms by which nuclear oncoproteins act remain unknown. Recently, an oncogene, v-jun, was found to share homology with the DNA binding domain of a yeast transcription factor, GCN4. Furthermore, GCN4 and the phorbol ester-inducible enhancer binding protein, AP-1, recognize very similar DNA sequences. The human proto-oncogene c-jun has now been isolated, and the deduced amino acid sequence indicates more than 80 percent identity with v-jun. Expression of cloned c-jun in bacteria produced a protein with sequence-specific DNA binding properties identical to AP-1. Antibodies raised against two distinct peptides derived from v-jun reacted specifically with human AP-1. In addition, partial amino acid sequence of purified AP-1 revealed tryptic peptides in common with the c-jun protein. The structural and functional similarities between the c-jun product and the enhancer binding protein suggest that AP-1 may be encoded by c-jun. These findings demonstrate that the proto-oncogene product of c-jun interacts directly with specific target DNA sequences to regulate gene expression, and therefore it may now be possible to identify genes under the control of c-jun that affect cell growth and neoplasia.

Amino Acid Sequence↗
PubMed1987

Only two of the four sites of interaction with nuclear factors within the Xenopus U2 gene promoter are necessary for efficient transcription.

An analysis, performed by DNase I footprinting, of the interactions between factors present in Molt-4 nuclear extracts and a Xenopus U2 snRNA gene promoter is presented. Four distinct regions of sequence-specific DNA-factor interaction are found. Two of these correspond to the previously identified proximal and distal sequence elements (PSE and DSE) of the promoter. Both of these elements are important in U2 transcription, indicating a functional role for the observed interactions. The other two sites of interaction correspond to a sequence element conserved in many, but not all, vertebrate U snRNA gene promoters (the MSE) and to a region adjacent to the site of transcription initiation (the "cap site"). Site-directed mutants of these latter two elements are constructed which no longer bind nuclear factors. Transcriptional analysis in Xenopus oocytes reveals that these mutants are transcribed as efficiently as wild-type U2. Other possible roles for the two factors are discussed.

Animals↗
PubMed1986

Nuclear factors binding specific sequences within the immunoglobulin enhancer interact differentially with other enhancer elements.

The mouse immunoglobulin heavy chain (IgH) enhancer represents a cis essential control element that confers lymphoid-specific expression. Based on in vivo and in vitro competition experiments, as well as on in vivo dimethylsulfate (DMS) protection experiments, it has been inferred that cellular factors interact in trans with IgH enhancer sequences. In addition, transcription is stimulated in vitro by up to one order of magnitude in the presence of IgH enhancer sequences on an appropriate template. Thus, at least some of these factors have to be present in nuclear extracts. To examine the factors interacting with this lymphoid-specific enhancer in more detail we compared the binding pattern of nuclear factors present in B-cell, T-cell and HeLa cell extracts. We demonstrate here, using the DNase I and DMS protection methods, the specific interaction of three different nuclear factors with the central PstI--EcoRI fragment of the IgH enhancer. This fragment has previously been suggested to retain the major enhancing activity. Surprisingly, no or only minor differences were discovered when the footprints obtained with B-cell extracts were compared with those obtained with HeLa cell and T-cell extracts. Intriguingly, two factors binding specifically to different sequences of the IgH enhancer are shared by polyoma as well as Moloney sarcoma virus (MSV) and lymphotropic papova virus (LPV) enhancer, respectively. All three of these enhancer elements exhibit altered cell type specificities. This indicates the utilization of similar or identical factors for transcriptional enhancement in different cell types. A cassette model consisting of different factor binding sites will be discussed.

B-Lymphocytes↗
PubMed1985

The SV40 enhancer influences viral late transcription in vitro and in vivo but not on replicating templates.

We have examined transcription from the SV40 late promoter in vitro and in vivo. In HeLa whole cell extracts, late transcription is efficient in the absence of T antigen but is impaired by enhancer specific point mutations. In vivo, when replication is prevented, transcription from the late promoter requires T antigen as well as a functional enhancer. However, enhancer sequences fail to potentiate late transcription from replicating templates although, under such conditions, enhancer binding factors do not become limiting. It appears that the SV40 late transcription unit is refractory to enhancer-mediated activation when it is located on a replicating template.

Antigens, Polyomavirus Transforming↗
PubMed1984

A transcription enhancer acts in vitro over distances of hundreds of base-pairs on both circular and linear templates but not on chromatin-reconstituted DNA.

We have analyzed the effect of nucleosome formation and of the simian virus (SV40) enhancer on the efficiency of in vitro transcription. In a whole cell extract made from HeLa cells, nucleosome assembly on DNA results in the formation of chromatin-like complexes. However, transcription was detectable only when the DNA templates were partially or totally depleted of nucleosomes. On nucleosome-free templates, when the SV40 enhancer was present upstream from the complete SV40 early or rabbit beta-globin promoters, there was a five- to tenfold stimulation of specific transcription. When present upstream from its homologous promoter, the SV40 enhancer activated SV40 early transcription independently of its orientation with respect to the coding sequence. Point mutations known to impair the SV40 enhancer function in vivo had a similar effect in vitro. The extent of the enhancing effect was the same with linear or circular templates. When the SV40 enhancer was inserted upstream from the rabbit beta-globin gene, the activation of transcription was reduced with increasing distance between the enhancer and beta-globin upstream promoter elements, but was still significant over a distance of more than 400 base-pairs.

Chromatin↗
PubMedDate not supplied

A transcription factor which binds to the enhancers of SV40, immunoglobulin heavy chain and U2 snRNA genes.

In eukaryotes the transcriptional control of RNA polymerase II-mediated gene expression is exerted by cis-acting regulatory DNA elements classified as promoter and enhancer sequences. These elements are composed of a number of different protein binding sites. The regulatory factors that recognize such 'modules' may be ubiquitous, tissue- or stage-specific, and positively or negatively acting. According to this model the transcriptional activity of a given gene is programmed by a combination of different modules. We analysed such a site of protein-DNA interaction, the octamer motif, in the enhancers of the simian virus (SV40) early genes and the murine immunoglobulin heavy-chain gene, and in the distal sequence element (DSE) of the U2 small nuclear (sn)RNA gene of Xenopus laevis. The corresponding DNA-binding factor appears to be the same in the three cases. Moreover, a fraction containing partially purified octamer motif binding factor has a stimulatory effect on transcription in an in vitro system.

Animals↗