Timing and induction of hsp70 production in Chlamydomonas reinhardtii
1994
Adams, M. | Savino, E. (Eastern Connecticut State Univ., Willimantic (USA). Biology Department) | Freeman, M.
Chlamydomonas responds to a short-term (1-6 hours) temperature increase from 20 deg C to 40 deg C by producing several specific heat shock proteins (hsp), with molecular weights of 96, 88, 80, 72, 38, and 22 kDa. The appearance of the proteins is not a signal of cell death, since survival at 42 deg C leads to almost total lethality. Although the appearance of all these proteins seems to be synchronous we have concentrated on that with a molecular weight of 72 kDa because it is likely that it is a member of the almost universal hsp 70 family of heat shock proteins. These "chaperone proteins" are believed to aid the folding and final interactions of newly synthesized proteins in the cell. Initial experiments to determine the time-course of hsp70 production show that it is made early in the heat shock, with the bulk being synthesized in the 1st hour. Once this protein has been synthesized it is stable for at least 6 hours, both at 20 deg C and 40 deg C. In order to test whether it is the temperature increase per se, or the relative amount of free hsp70 in the cell that signals its induction, cells were exposed to 2 successive heat shocks, with a recovery period in between. The results show that the 2nd shock does not induce additional hsp70 production. This supports the idea that hsp70 is normally in equilibrium with other cellular proteins and that the destabilizing effect of heat shock means that more hsp70 must be made to compensate.
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