YEAST HEAT-SHOCK TRANSCRIPTION FACTOR CONTAINS A FLEXIBLE LINKER BETWEEN THE DNA-BINDING AND TRIMERIZATION DOMAINS - IMPLICATIONS FOR DNA-BINDING BY TRIMERIC PROTEINS

All heat shock transcription factors (HSFs) share two regions of homol ogy, identified as the DNA binding and trimerization regions. The DNA binding region consists of two parts, an 89-amino-acid minimal DNA-bin ding domain and an additional 21 amino acids which are not necessary f or specific DNA binding of a monomeric DNA-binding domain. These 21 am ino acids may act as a flexible linker between the DNA-binding and tri merization domains. Saccharomyces cerevisiae HSF has an additional 52 amino acids between the proposed flexible linker and the trimerization domain. Deletion of this unique region has no effect on the structura l integrity or essential in vivo functions of HSF. To investigate the role of the 21-amino-acid proposed linker a series of internal deletio ns was created in fragments containing the DNA-binding and trimerizati on domains. The deletions have no effect on the structural integrity o f the protein as assayed by circular dichroism spectroscopy. However, alterations of the linker do affect affinity of trimeric HSF binding t o its target DNA In addition, deletion of part or all of the proposed linker from full-length yeast HSF, an essential protein, disrupts grow th of yeast.