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Gene transcription can be regulated by promoter competition when multiple promoters are available for a single enhancer. The converse, however, is largely undescribed. Here we report an occurrence of several enhancers competing for one promoter (enhancer interference) and propose its underlying mechanism. The promoter targeting sequence from the AbdominaI-B locus of the Drosophila bithorax complex overcomes the enhancer-blocking activity of insulators in transgenic embryos. It may facilitate the long-range enhancer-promoter communication in Abdominal-B by bypassing insulator elements such as Frontabdominal-7 and Front-abdominal-8. In transgenic embryos, the anti-insulator activity allowed both an insulator-blocked enhancer and a nonblocked enhancer to contact the same promoter. We found that these two enhancers exhibited mutual inhibition or mutual exclusion in cells where both are transcriptionally active. This enhancer interference occurred at the level of enhancer-promoter communication. It occurred only between enhancers on opposite sides of an insulator and depended on enhancer activity. We hypothesize that enhancer interference limits the interaction of the AbdominaI-B promoter to the enhancer(s) from only one regulatory domain in a specific abdominal segment. Abd-B | Fab-8 | IAB8 | NEE

The research makes use of a structure model, in addition to the various energy transfer distance measurements to study the T7 RNA polymerase, which causes bending of its promoter DNA on binding by various proteins and other complexes. The analysis proves the existence of a bent and an open model for the initiation complex of T7 and also shows that in spite of the massive changes, the DNA of the active site is very much identical in initiation as well as elongation complexes.

A novel mode of interaction between ubiquitin and the cyclin-dependent kinase subunit of Saccharomyces cerevisae, Cks1p, an adaptor protein involved in transcriptional regulation through recruitment of proteasomal subunits to gene promoters is reported. Cks1p interacts specifically with monoubiquitin and tetraubiquitin with an affinity several orders of magnitude greater than that of other ubiquitin-binding domains.

Fluorescence resonance energy transfer (FRET) is used to investigate the conformation of promoter DNA in the closed and open complexes of T7 RNA polymerase (T7 RNA P). It is proposed that promoter opening occurs spontaneously upon DNA bending and/or untwisting as free energy is gained through interactions of the melted promoter with the T7 RNAP active site.

Elucidation of the temporal coupling in DNA binding, bending, and opening processes that occur during initiation is presented. The results provided are consistent with the mechanism in which the initial binding of T7 RNAP to the promoter results in a closed complex, which is then converted into an open complex in which promoter is both sharply bent and melted.