Regulation of heat‐shock protein synthesis in chicken muscle culture during recovery from heat shock

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Abstract
Exposure of chick myotube cultures to a temperature (45.degree. C) higher than their normal growing temperature (37.degree. C) caused extensive synthesis of 3 major polypeptides of MW = 25,000, 65,000 and 81,000 referred to as heat-shock polypeptides (hsp). When these cells were allowed to recover from heat-shock treatment at 37.degree. C for 6-8 h, the rate of accumulation of isotope into the 65,000-MW and 81,000-MW hsp declined to levels comparable to those in control cultures maintained at 37.degree. C. Incorporation of isotope in the 25,000-MW hsp continued at an elevated rate for a longer period than the 65,000-MW and 81,000-MW hsp. When heat-shocked cells were allowed to recover at 37.degree. C in the presence of actinomycin D to block new mRNA synthesis, the hsp synthesis as measured by the incorporation of radioactive isotope in these polypeptides continued at levels comparable to those in heat-shocked cells prior to recovery. The block of recovery by actinomycin D was due to the presence of a greater amount of functional hsp mRNA in the polysomes as compared to untreated controls. The role of competition between the mRNA for hsp and normal cellular proteins for the translation machinery in regulating protein synthesis during the recovery from heat shock was discussed.