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We have isolated and characterized a 91 amino acid fragment of the heat shock transcription factor from both Saccharomyces cerevisiae and Kluyveromyces lactis. The two protein fragments behave similarly: they form homotrimers, as indicated by sedimentation equilibrium and cross-linking, and contain approximately 80% alpha-helix, as indicated by circular dichroism. Sedimentation velocity and diffusion coefficients indicate that they have an elongated, nonspherical shape. We conclude the following: these fragments contain a domain which forms a trimer via a triple-stranded alpha-helical coiled-coil, similar to that found in influenza hemagglutinin.
Peteranderl et al. (1992) studied this question.