Cell
Volume 64, Issue 3, 8 February 1991, Pages 585-593
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Article
Cooperative binding of drosophila heat shock factor to arrays of a conserved 5 bp unit

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Abstract

Drosophila heat shock factor (HSF) exists as a multimer in solution and when bound to its regulatory element (HSE). We have previously reported evidence that subunits of HSF associate to form homotrimers and that each subunit contacts a conserved 5 by DNA sequence repeated within an HSE. Here we show that HSF binding is highly cooperative at two distinct levels: between subunits of the HSF multimer, and between multimers. The binding of HSF to one of a pair of adjacent trimeric binding sites facilitates HSF binding to the second by over 2000-fold. This cooperativity is particularly Important in binding HSF at 37°C, and could account for the requirement for multiple binding sites in vivo and, in part, for the differential expression of heat shock genes.

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Present address: Waksman Institute, Rutgers State University, Piscataway, New Jersey 08855.