Heat shock factor 1 is a key regulator of the stress response in Chlamydomonas

We report here on the characterization of heat shock factor 1 (HSF1), encoded by one of two HSF genes identified in the genome of Chlamydomonas reinhardtii. Chlamydomonas HSF1 shares features characteristic of class A HSFs of higher plants. HSF1 is weakly expressed under non-stress conditions and rapidly induced by heat shock. Heat shock also resulted in hyperphosphorylation of HSF1, and the extent of phosphorylation correlated with the degree of induction of heat shock genes, suggesting a role for phosphorylation in HSF1 activation. HSF1, like HSFs in yeasts, forms high-molecular-weight complexes, presumably trimers, under non-stress, stress and recovery conditions. Immunoprecipitation of HSF1 under these conditions led to the identification of cytosolic HSP70A as a protein constitutively interacting with HSF1. Strains in which HSF1 was strongly under-expressed by RNAi were highly sensitive to heat stress. 14C-labelling of nuclear-encoded proteins under heat stress revealed that synthesis of members of the HSP100, HSP90, HSP70, HSP60 and small HSP families in the HSF1-RNAi strains was dramatically reduced or completely abolished. This correlated with a complete loss of HSP gene induction at the RNA level. These data suggest that HSF1 is a key regulator of the stress response in Chlamydomonas.     

人热休克因子1突变体的应用研究进展

热休克因子1是调节应激反应的主要转录因子,它在应激条件下可被活化。通过基因突变得到正显性和负显性热休克因子1,它们不需要外界条件刺激就分别具有启动热休克蛋白的表达或竞争抑制内源热休克因子1活性的能力。目前,已有多个热休克因子1的突变体应用于疾病研究。介绍了热休克因子1的结构和活化途径,以及热休克因子1突变体在肿瘤、神经系统及心血管系统等方面的应用进展。     

Interaction of the Neurospora crassa heat shock factor with the heat shock element during heat shock and different developmental stages

The interaction of the heat shock factor (HSF) with the heat shock element (HSE) was determined by a non-radioactive electrophoretic mobility shift assay, in order to analyze HSF regulation in Neurospora crassa. HSF binds to HSE under normal, non-stress conditions and is thus constitutively trimerized. Upon heat shock, the HSF-HSE complex shows a retarded mobility. This was also observed in Saccharomyces cerevisiae, where this mobility shift was shown to be due to HSF phosphorylation [Sorger and Pelham (1988) Cell 54, 855-864]. In N. crassa, HSE-dependent electrophoretic mobility shift is temperature- and time-dependent. Under normal growth conditions, the HSF is located in the cytoplasm as well as in the nucleus. In germinating conidia the HSF shows a retarded mobility typical for heat shock even at normal growth temperatures. No HSF-dependent mobility shift was detectable in aerial hyphae.