FIGURE 4:

As(III) acts at the level of the Ptp2 and Ptp3 tyrosine phosphatases. (A) The basal phosphorylation of Hog1 is elevated strongly in the absence of the protein phosphatases that down-regulate it. Comparison of wild-type (DL2772), ptp2∆ ptp3∆ (DL4299), and a ptp2∆ ptp3∆ ptc1∆ mutant (DL4309) for Hog1 phosphorylation status. (B) As(III) fails to activate Hog1 in protein phosphatase mutants. The same mutant strains as above were tested for activation of Hog1 by 1 mM As(III) or 400 mM NaCl to induce hyperosmotic shock for the indicated times. (C) Mutations in PTP2 and PTP3 confer tolerance of As(III). Wild-type cells (DL2772), ptp2∆ (DL4295), ptp3∆ (DL4296), ptc1∆ (DL4297), ptp2∆ ptp3∆ (DL4299), and ptp2∆ ptp3∆ ptc1∆ (DL4309) were spotted onto YPD plates with or without 4 mM As(III) at serial 10-fold dilutions (from left to right). Plates were incubated at 30°C for 2 d.