HEAT-SHOCK RESPONSE OF THE HALOALKALIPHILIC ARCHAEON NATRONOBACTERIUM-MAGADII

Heat-shock response was studied at increased growth temperature (50, 5 5 and 60 degrees C) for the haloalkaliphilic archaeon Natronobacterium magadii. Protein synthesis was monitored by [S-35]methionine incorpor ation into proteins at the various temperatures. The rate of synthesis of most cellular proteins at 50 degrees C was slightly decreased, whi le the synthesis of a protein group with molecular masses ranging from 95 to 105 kD was increased. Protein synthesis at 55 degrees C was rep ressed, and only six proteins with a molecular masses of about 40, 50, 65, 70, 105, and 140 kD continued to be synthesized. The synthesis of the 105 kD protein (Hsp105) at this temperature was 10 times higher t han at 37 degrees C. Only Hsp 105 synthesis was still found at 60 degr ees C; this may be due to complete cell lysis at 60 degrees C. It was also shown that Hsp105 is a cytosolic protein which does not form larg e multi-protein complexes like chaperonins. Also no ATPase activity fo r Hsp105 was found.