The constitutive and the heat-shock-induced expression of members of heatshock protein families changed during vegetative development and conidiation of Neurospora crassa as determined by two-dimensional gel electrophoresis. Western blot and ELSA analyses revealed the highest amounts of the constitutive heat-shock protein 70 (HSC70) in conidiating aerial hyphae and dormant conidia. During conidial germination the amount of HSC7O decreased and subsequently increased during vegetative growth. Stationary mycelia and young aerial hyphae exhibited the lowest HSC7O level. The stationary-phase-dependent decrease in HSC70 was accompanied by a concomitant increase in i t s nuclear localization, whereas no significant changes in the amount of nuclear HSC7O were found during aerial hyphae development. The CAMP content during aerial hyphae development was inversely correlated with that of HSC7O. To examine possible causal relations between HSC70 expression and CAMP content, the adenylate-cyclase-def icient mutant crisp (cr-I) was analysed, which exhibits low concentrations of endogenous CAMP. This mutant, however, showed a lower constitutive HSC7O level, compared to the bdA strain. Treatment of the bd strain and cr-I mutant with 20 pM 8-bromo-CAMP did not result in significant changes of the constitutive HSC7O level, but in the level of heat-induced HSOHSP70. In a developmental mutant (acon-2) which is defective in a differentiation step toward conidiation, the expression of HSC7O in aerial hyphae was delayed until the first proconidial chains were observed. It is concluded that the differential expression of HSUHSP7O does not depend on different nuclear levels of HSC7O or on changes in CAMP concentrations, but rather on developmental genes controlling conidiation.

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In Neurospora crassa the aliphatic alcohols methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, ethylene glycol, glycerol, and allyl alcohol and the phenolic compounds phenol, hydroquinone, resorcinol, pyrogallol, phloroglucinol, sodium salicylate, and acetylsalicylic acid were analyzed with respect to their capacities to induce heat shock proteins (HSP) and to inhibit protein synthesis. Both the alcohols and phenols showed the greatest levels of HSP induction at concentrations which inhibited the overall protein synthesis by about 50%. The abilities of the different alcohols to induce the heat shock response are proportional to their lipophilicities: the lipophilic alcohol isobutanol is maximally inductive at about 0.6 M, whereas the least lipophilic alcohol, methanol, causes maximal induction at 5.7 M. The phenols, in general, show a higher capability to induce the heat shock response. The concentrations for maximal induction range between 25 mM (sodium salicylate) and 100 mM (resorcinol). Glycerol (4.1 M) shifted the concentration necessary for maximal HSP induction by hydroquinone from 50 to 200 mM. The results reveal that the induction of HSP occurs under conditions which considerably constrain cell metabolism. The heat shock response, therefore, does not represent a sensitive marker for toxicity tests but provides a good estimate for the extent of cell damage.

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