Msn2

Msn2 is a zinc finger protein that regulates, in parallel with its homolog Msn4, stress-responsive genes through interaction with the STress Response Element AGGGG (Boy-Marcotte et al., 1998; Martinez-Pastor et al., 1996; Schmitt and McEntee, 1996). Msn2 is primarily regulated at the level of nuclear exclusion, accumulating in the nucleus only upon the cell’s exposure to environmental stresses such as heat shock, glucose starvation, osmotic stress, or treatment with rapamycin (Beck and Hall, 1999; Gorner et al., 1998).

Msn2 is phosphorylated in vitro by protein kinase A (Chi et al., 2001; Garreau et al., 2000). In vivo, carbon starvation and heat shock result in two different forms of phosphorylated Msn2 (Garreau et al., 2000), with the former leading to modification of the regulator’s nuclear localization domain (Gorner et al., 2002).

Nuclear concentrations of Msn2 are not only controlled by translocation of Msn2 into the nucleus, but also by its regulated export. The exportin Msn5 is required to exclude Msn2 from the nucleus under non-stress conditions (Chi et al., 2001). It has been suggested that this export is dependent on hyperphosphorylation of a nuclear export domain by Srb10 (Chi et al., 2001; Gorner et al., 2002).