Analysis of promoters of adenovirus type 12 E1A gene in a cell-free transcription system

Transcription stimulation of the adenovirus type 12 E1a gene in vitro by the 266-amino-acid E1A protein

We previously showed that the 13S but not the 12S mRNA product of the E1a gene of the highly oncogenic type 12 adenovirus (Ad12) stimulates the expression of its own gene. In this study, the mechanism for the autoregulation of the Ad12 E1a gene was investigated in vitro. The 266-amino-acid E1A protein of Ad12 was synthesized in yeast cells and purified as a 57-kDa polypeptide. The purified Ad12 E1A protein stimulated transcription from the proximal promoter of its own gene but had almost no effect on that from the distal promoter. A 35-bp upstream region including a TATA box for the proximal promoter seemed to be sufficient for transcription stimulation by the E1A protein. The Ad12 E1A protein formed a complex with a TATA box-binding protein (TBP), as does the E1A protein of nononcogenic Ad serotypes. Moreover, the E1A protein significantly reduced the binding of TBP to a TATA sequence, while it did not affect the DNA-binding activity of nuclear factor I, a stimulatory protein of the distal transcription of the Ad12 E1a gene. These results suggest that the 13S mRNA product of the Ad12 E1a gene regulates the transcription of its own gene by modulating the activity of TBP.

Multiple cis-acting DNA elements that regulate transcription of the adenovirus 12 E1A gene

To delineate cis-acting elements for adenovirus (Ad) 12 E1A gene transcription, we transfected HeLa and NIH3T3 cells with DNAs having various deletions in the 5'-upstream region linked to the chloramphenicol acetyltransferase gene. Deletions in the regions between nucleotide (nt) positions 54 and 166, and 167 and 200, with respect to the left end of the viral genome at nt position 1, caused a two- to three-fold reduction in transcription. Transcription decreased to an almost undetectable level with loss of the region between nt positions 201 and 282. The effect of these mutations was almost consistent between both cell lines. The region between nt positions 77 and 94 stimulated transcription when situated upstream of the simian virus 40 early promoter in either orientation. Transcription was stimulated about ninefold in the presence of the DNA that encodes the product of the 13S, but not the 12S mRNA of the Ad12 E1A gene. These results indicate that transcription of the Ad12 E1A gene is regulated by multiple cis-acting elements and is stimulated by its own gene product.

Direct effect of basic fibroblast growth factor on gene transcription in a cell-free system

Recent findings on the translocation of intact fibroblast growth factor (FGF) into the cell nucleus suggest that it functions directly in nuclear events. We examined the effect of human basic FGF (bFGF) on gene transcription in a cell-free system. When mouse genes encoding phosphoglycerate kinases 1 and 2 (Pgk-1 and Pgk-2) were transcribed by using nuclear extracts of Ehrlich ascites tumor cells, FGF affected transcription in different ways: in the presence of bFGF, transcription of the Pgk-1 gene was inhibited, whereas that of the Pgk-2 gene was enhanced. When viral genes were tested, transcription of the adenovirus major late DNA was slightly stimulated but that of the adenovirus early E1A DNA or the human immunodeficiency virus DNA was not changed by the addition of bFGF. Moreover, the presence of a distinct 5' upstream region of the Pgk-2 gene, which includes a negative cis-acting element, was required for transcription stimulation by bFGF. These results suggest that bFGF can regulate transcription directly in the nucleus in a gene-specific manner.

Transcription stimulation of the adenovirus type-12 E1a gene in vitro by a novel factor bound to a region adjacent to a TATA box

The E1a gene of adenovirus (Ad) type-12 possesses two transcription start points (tsp) separated by 139 nucleotides (nt). We previously found that transcription from a tsp distal to the coding region is preferentially stimulated in a cell-free reaction by nuclear factor I (NF-I) bound to a region near the left end of the virus genome. We report here on the identification of a cis-acting DNA region and a trans-acting factor for transcription initiated at the proximal tsp of the Ad12 E1a gene. A deletion in the region between nt -50 and -36 relative to the proximal tsp at +1 caused a significant decrease in the proximal transcription in a cell-free reaction using nuclear extracts of HeLa cells. A cellular factor binding to this region was shown to be responsible for transcription stimulation. This E1A-stimulating factor (ESF-1) appeared to recognize the sequence 5'-TGTCA-3' located immediately upstream from a TATA box. Unlike NF-I, the ESF-1 activity did not seem to be influenced by the E1A protein. Our results indicated that ESF-1 stimulates the proximal transcription of the Ad12 E1a gene by binding to the region adjacent to a TATA box.

A novel cis-acting element that controls transcription of human immunodeficiency virus type 1 DNA, depending on cell type

cis-acting elements for the transcription of human immunodeficiency virus type 1 DNA were analyzed in cell-free transcription and DNA transfection assays. Besides previously identified cis elements, a region adjacent to the enhancer element was found to regulate transcription in both assays. Loss of this region caused 4.3- and 1.6-fold transcription inhibition in a transfection assay with a T-cell line, MOLT-4, and a monocyte line, U937, respectively, whereas the same region appeared to function negatively with other T-cell lines, MT-4 and Jurkat. These results suggest that this novel cis element regulates the transcription of proviral DNA in a cell-type-specific manner.

Nuclear factor I stimulates transcription of the adenovirus 12 E1A gene in a cell-free system

Binding to the cis-acting region of NF-I-like protein and/or NF-III-like protein was previously suggested to be responsible for the preferential stimulation of transcription from distal start-site of the adenovirus 12 E1A gene in a cell-free system. In this study, nuclear extracts of Ehrlich ascites tumor cells depleted of NF-I-like protein were found to lose activity to stimulate the E1A gene transcription. This activity was recovered when NF-I purified from HeLa cells with no contamination of NF-III was supplemented. It is thus evident that NF-I is involved in stimulating distal transcription of the adenovirus 12 E1A gene. Moreover, activities for both stimulating the E1A gene transcription and binding to a region recognized by NF-I did not apparently exist in nuclear extracts of a cell line expressing the adenovirus 12 E1A gene. These results suggest that transcription of the adenovirus 12 E1A gene may possibly be autoregulated at least in part through modulation of the activity of NF-I.

Cis- and trans-acting factors for transcription of the adenovirus 12 E1A gene

Cis- and trans-acting factors were analyzed for transcription of the adenovirus 12 E1A gene possessing two sites for transcription initiation. These sites are located at nucleotide positions 306 and 445 with respect to the left end of the viral genome as position 1. The template activity of DNAs with various deletions at the 5'-upstream region of the E1A gene was examined in a cell-free system using a nuclear extract of Ehrlich ascites tumor cells. A DNA region specifically stimulating transcription initiated at the site distal to the E1A coding sequence was found located between positions 1 and 166. No DNA sequence affecting transcription from a proximal start-site appeared to be present in the region between positions 1 and 378. DNaseI-footprinting indicated that factors present in the extract bind to two distinct DNA segments, both of which are located within a region stimulating distal transcription. Two footprints were observed, one between positions 19 and 55 and the other between 77 and 94. The former footprint was inhibited by synthetic oligonucleotides containing a sequence recognized by nuclear factor I and the latter contained a sequence similar to one present in the B-enhancer of polyoma virus. Competition of in vitro transcription with synthetic oligonucleotides indicated (a) nuclear factor(s) bound to the region between positions 19 and 55 to be responsible for stimulating distal transcription of the adenovirus 12 E1A gene.

Interactions of factors bound at two different sites in the 5'-upstream region of the adenovirus 12 E1A gene

A nuclear extract of Ehrlich ascites tumor cell contains factors binding to two distinct sites in the 5'-upstream region of the adenovirus 12 E1A gene. The gel shift assay was performed for characterization of the binding factors with oligo DNA probes containing sequences corresponding to these sites. The specific binding of a factor to one probe was enhanced when the other oligo DNA was present in excess in the binding reaction. Thus possibly, protein-protein interactions between factors may mutually prevent their binding to target sequences.