Study on simultaneous yet independent regulation of actin cytoskeletal organization and translation initiation by environmental stress

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Acute glucose deprivation rapidly but transiently depolarizes the actin cytoskeleton and inhibits translation initiation in Saccharomyces cerevisiae. Neither rapid actin depolarization nor translation inhibition upon glucose removal occurs in a reg1 disruptant, which is defective in glucose repression, or in the tpk1^w mutant, which has weak cAPK activity. In the absence of additional glucose, recovery of either actin polarization or translation initiation relies upon respiration, the Snf1p protein kinase, and the transcription factors Msn2p and Msn4p. The readdition of glucose to glucose-starved cells causes a rapid recovery of actin polarization as well as translation initiation without respiration. These results indicate that the simultaneous regulation of actin polarization and translation initiation is divided into three reactions : (1)rapid shutdown depending on Reg1p and cAPK after glucose removal, (2)slow adaptation depending on Snf1p and Msn2p/4p in the absence of glucose, and (3)rapid recovery upon readdition of glucose. Upon glucose removal, translation initiation is rapidly inhibited in a rom2 disruptant, which is defective in rapid actin depolarization, whereas rapid actin depolarization occurs in a pop2/caf1 disruptant, which is defective in rapid inhibition of translation initiation. Thus, translation initiation and actin polarization appear to be simultaneously but independently regulated by glucose deprivation.