TEMPERATURE ADAPTATION OF HOUSE KEEPING AND NEAT SHOCK GENE-EXPRESSION IN NEUROSPORA-CRASSA

Temperature adaption of house keeping and heat shock gene expression i n Neurospora crassa, Fungal Genetics and Biology 25, 31-43. Adaptation of house keeping and heat shock gene expression was determined in Neu rospora crassa during continuous exposure to different temperatures. S teady-state values of total protein synthesis differed little after in cubation for 24 h at temperatures between 15 and 42 degrees C, Adaptat ion kinetics at 42 degrees C showed an initial, transient inhibition o f total protein synthesis. Similar kinetics were observed with actin s ynthesis and tubulin mRNA. A priming 1-h heat shock of 42 degrees C 2 h prior to a second continuous exposure to 42 degrees C abolished the inhibitory effect of the second treatment and resulted in ''acquired t ranslational tolerance.'' Steady-state values of HSP70 synthesis rates revealed increasing levels with increasing temperatures after incubat ion for 24 h at different temperatures. Adaptation kinetics of the syn thesis rates of different HSPs in vivo revealed maximal rates after 2 h and then a decrease to the elevated steady-state levels. The total a mount of the major constitutive and inducible HSP70 isoform as determi ned by Western blots reached a maximum 2 h after the beginning of 42 d egrees C exposure and only a slight decrease (25%) of the maximal valu e after 24 h. The inducible isoform of HSP70, in contrast, reached a m aximum after 4-8 h and then decreased strongly after 24 h, HSP mRNAs r eached maximal amounts 45-60 min after the beginning of 42 degrees C e xposure and then declined after 8 h as determined by in vitro translat ion. Northern blots revealed maximal mRNA amounts of the inducible HSP 70 after 30 min and zero amounts after 4 h exposure to 42 degrees C. A fter a shift to 42 degrees C HSP70 isoforms were immediately transloca ted into the nucleus and reshuttled into the cytoplasm during the foll owing 6 h. The nuclear content of HSP70 remained elevated during the a dapted steady state at 24 h. It is concluded that the adapted state af ter 24 h is based on enhanced amounts of constitutive isoforms in the cytoplasm and in the nucleus, whereas the inducible isoforms of HSP70 show faster adaptation kinetics. (C) 1998 Academic Press.