Discrete elements within the SV40 enhancer region display different cell-specific enhancer activities.

Abstract

The SV40 enhancer contains three genetically defined elements, called A, B and C, that can functionally compensate for one another. By using short, synthetic DNA oligonucleotides, we show that each of these elements can act autonomously as an enhancer when present as multiple tandem copies. Analysis of a progressive series of B element oligomers shows a single element is ineffective as an enhancer and that the activity of two or more elements increases with copy number. Assay in five different cell lines of two separate enhancers containing six tandem copies of either the B or C element shows that these elements possess different cell‐specific activities. Parallel oligomer enhancer constructs containing closely spaced double point mutations display no enhancer activity in any of the cell lines tested, indicating that these elements represent single units of enhancer function. These elements contain either a ‘core’ or ‘octamer’ consensus sequence but these consensus sequences alone are not sufficient for enhancer activity. The different cell‐specific activities of the B and C elements are consistent with functional interactions with different trans‐acting factors. We discuss how tandem duplication of such dissimilar elements, as in the wild‐type SV40 72‐bp repeats, can serve to expand the conditions under which an enhancer can function.

Enhancers, enhancers – from their discovery to today’s universe of transcription enhancers

“…As the building blocks of enhancer activity are short DNA sequence motifs, synthetic, highly active enhancers can be constructed that consist of multiple binding sites for just one type of transcription factor (Gerster et al, 1987;Ondek et al, 1987;Schatt et al, 1988). Such monotonous enhancers do not occur in nature because they would not be compatible with a sophisticated regulation by different transcription factors and signaling pathways.…”

An endocrine-specific element is an integral component of an exocrine-specific pancreatic enhancer.

“…Any unexpected activities uncovered can be verified within the normal context of the enhancer. This approach has been successful for characterizing the binding sites for single transcription factors within complex viral {Veldman et al 1985;Ondek et al 1987;Schirm et al 1987} andcellular (Meister et al 1989) enhancers by cell transfection and for pattern-forming transcriptional elements reintroduced into Drosophila embryos (Vincent et al 1990}. In addition, the interleukin-2 gene element that mediates transcriptional induction by the nuclear factor of activated T cells (NFAT-1) has been shown to be active as a homomultimer in transgenic mice (Verweij et al 1990}.…”

YB-1 binds to the MMP-13 promoter sequence and represses MMP-13 transactivation via the AP-1 site

“…We speculate that binding of YB-1 to AP-1 oligos such as the GALV or 4XAP-1 would be more readily detectable in gel shift than binding to the MMP-13 1X AP-1 site because the tandem YB-1 binding sites that are present in GALV or 4XAP-1 afford them higher affinity for YB-1 binding. Multimerized tandem binding sites have been shown in early seminal studies by Winship Herr's laboratory to markedly augment activity of transcription factors at their DNA binding sites [30,31]. YB-1 is a very abundant nuclear protein in a number of malignant cell types [20].…”