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When rabbit reticulocytes are incubated at 43–45°C their rate of protein synthesis rapidly decreases, compared to a control 37°C incubation. Lysates prepared fi'om cells incubated at this supra-optimal temperature have an equally decreased capacity for endogenous, but not poly(uridylic acid)-directed, protein synthesis. Subcellular fractionation traced the lesion to the crude ribosomal pellet, 0.5 M KCl ribosomal wash and postribosomal supernatant of the temperature-shocked cells. Preparation of purified ribosomal subparticles showed, however, that they were as active as the control in protein synthesis. In this paper we present evidence that the decreased activity of the heated lysate, 0.5 mM KCl wash and postribosomal supernatant is due to an inhibitor and can be overcome by the addition of 0.5 M KCl or supernatant from control cells. The results are discussed in terms of the inactivation of a component, essential for initiation of endogenous protein synthesis, which is probably partitioned between ribosomes and supernatant. We also suggest that the decreased protein synthetic activity of the heated cells may be related to their decreased synthesis of haem. [ABSTRACT FROM AUTHOR]

Translation of cellular and early vaccinia RNA in nuclease-treated lysates, derived from uninfected and vaccinia-virus-infected cells al the early stage, has been investigated. When using limiting amounts of RNA no discrimination of translation was observed in the infected cells lysates; This conclusion was confirmed by sensitive RNA competition experiments for translation in vitro and also when using two different fractionated systems for protein synthesis in vitro. This absence of detectable discrimination in vitro was established both by comparing incorporation of [35S]methionine into proteins and by analysis of the products thus synthesized by sodium dodecylsulfate gel electrophoresis. However, a modification of the translational machinery from vaccinia-virus-infected cells did occur since only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis of an early protein involved in translation or from a better recovery of translational factors from the infected cells., as suggested in the accompanying paper. [ABSTRACT FROM AUTHOR]