A CCAAT box confers cell-type-specific regulation on the Xenopus hsp70 gene in oocytes

The Xenopus hsp70 gene is transiently heat-inducible in somatic cells; in injected oocytes, it is efficiently expressed without heat shock. I show here that this cell-type-specific and gene-specific activation is dependent on the presence of a heat shock regulatory element (HSE) and a CCAAT box in the hsp70 promoter; neither element by itself is sufficient for full activation. The same promoter elements are also required for heat inducibility in somatic cells. I propose that CAAT-binding transcription factor (CTF) interacts with heat shock transcription factor (HSTF), thereby enhancing the affinity of HSTF for the promoter; cell-type specificity could be explained by assuming either oocyte-specific forms or oocyte-specific high levels of CTF and/or HSTF.