M. Fernandes et al., BINDING OF HEAT-SHOCK FACTOR TO AND TRANSCRIPTIONAL ACTIVATION OF HEAT-SHOCK GENES IN DROSOPHILA, Nucleic acids research, 23(23), 1995, pp. 4799-4804
Heat shock factor (HSF) binds to heat shock elements (HSEs) and the bi
nding can be highly cooperative. Here we report an analysis of binding
of Drosophila HSF to both native and synthetic heat shock regulatory
regions. We find that cooperative binding of HSF requires close proxim
ity, rather than helical alignment, of HSEs. Two or more trimeric HSEs
organized as contiguous 5 bp units show much higher levels of coopera
tivity than multiple but separated HSEs. We discuss these in vitro obs
ervations in the context of the in vivo status of heat shock genes und
er mild and full heat shock conditions. Finally, we show that the DNA
binding and trimerization domains alone may be sufficient for the full
level of binding cooperativity between HSF trimers. This last result
suggests that close proximity of HSEs for cooperative binding of HSF i
s a result of protein-protein interactions near the point of DNA conta
ct.