DECREASE OF PROTEIN SYNTHESIS AND BREAKDOWN OF POLYRIBOSOMES BY ELEVATED TEMPERATURE IN PHYSARUM POLYCEPHALUM

The plasmodium of the myxomycete, Physarum polycephalum, which grows rapidly at 27°, was subjected to heat shocks at 40° for periods of either 10 or 30 min. During these shocks, protein hydrolysates labeled with tritium were added to the nutrient media for a 10-min period; with the plasmodia that were shocked for 30 min, the hydrolysate was added during the last 10 min. the heat shock reduced the uptake of amino acids into protein by approximately 40% with the 10-min shock and by more than 70% with the 30-min shock. The heat shock also caused a reduction of polyribosomes of more than 50%. These results are consistent with the suggestion that heat shock interferes with protein synthesis by decreasing the amount of polyribosomes. © 1969.