EFFICIENT MAMMALIAN PROTEIN-SYNTHESIS REQUIRES AN INTACT F-ACTIN SYSTEM

The mammalian protein synthesizing system is highly organized in vivo, and its substrate, tRNA, is channeled throughout the translation proc ess, However, the cellular components responsible for this organizatio n are not known. To examine this question a series of studies was carr ied out using intact and permeabilized Chinese hamster ovary cells, We show that cold shock dramatically reduces the protein synthetic capac ity of these cells by as much as 95%, The loss of activity can be reve rsed by a short recovery period under conditions that allow energy met abolism to occur; transcription and translation during the recovery pe riod are not needed, While individual components of the translation ap paratus are not inactivated by the cold shock, the supramolecular orga nization of the system appears to be altered and F-actin levels are fo und to decrease, Resumption of protein synthesis during the recovery p eriod coincides closely with the restoration of F-actin to normal leve ls. Moreover, disruption of actin filaments, but not microtubules, als o leads to a major reduction in translation. These data support the co nclusion that the cellular microfilament network plays an important ro le in the structure and function of the translation system and that pe rturbations of this network can have profound effects on protein synth esis.