HEAT-SHOCK TRANSCRIPTION FACTOR-1 BINDS SELECTIVELY IN-VITRO TO KU PROTEIN AND THE CATALYTIC SUBUNIT OF THE DNA-DEPENDENT PROTEIN-KINASE

Heat shock transcription factor 1 (HSF1) functions as the master regul ator of the heat shock response in eukaryotes, We have previously show n that, in addition to its role as a transcription factor, HSF1 stimul ates the activity of the DNA-dependent protein kinase (DNA-PK). DNA-PK is composed of two components: a 460-kDa catalytic subunit and a 70- and 86-kDa heterodimeric regulatory component, also known as the Ku pr otein. We report here that HSF1 binds specifically to each of the two components of DNA-PK. Binding occurs in the absence of DNA. The comple x with the Ku protein is stable and forms at a stoichiometry close to unity between the Ku protein heterodimer and the active HSF1 trimer, T he binding is blocked by antibodies against HSF1. Our results show tha t HSF1 also binds directly, but more weakly, to the catalytic subunit of DNA-PK. Both interactions are dependent on a specific region within the HSF1 regulatory domain, This sequence is necessary but not suffic ient for HSF1 stimulation of DNA-PK activity. The ability of HSF1 to i nteract with both components of DNA-PK provides a potential mechanism for the activation of DNA-PK in response to heat and other forms of st ress.