DIFFERENT ACTIVATION DOMAINS STIMULATE TRANSCRIPTION FROM REMOTE (ENHANCER) AND PROXIMAL (PROMOTER) POSITIONS

We reported previously that the lymphocyte-derived octamer transcription factor 2A (Oct-2A or OTF-2A) activated both natural immunoglobulin promoters and synthetic promoters which contain the 'octamer' site, but was unable by itself to stimulate transcription from a remote enhancer position. Here we examine a larger set of transcription factors with respect to their proximal versus remote activation. Since a transcription factor may contain more than one activation domain, we have chosen to study the potential of individual activation domains in the context of fusion proteins that contain the DNA binding domain of GAL4. We have identified at least two distinct functional classes of transcriptional activation domains. 'Proximal' activation domains, exemplified by glutamine-rich domains of Oct-1, Oct-2A and Sp1, stimulate transcription only from a position close to the TATA box, usually in response to a remote enhancer. 'General' activation domains, derived from VP16, GAL4, p65 (NF-chiB), TFE3, ITF-1 and ITF-2, can activate transcription from remote as well as proximal positions. These domains contain many acidic amino acids and/or other features such as dusters of serine and threonine. The proline-rich activation domains of AP-2 and CTF/NF1 may represent a third class with considerable promoter activity and low but significant enhancer activity. Furthermore, activation domains of both the acidic and glutamine-rich types seem to have a modular structure, since duplicated subdomains can substitute for the entire domain.