We previously reported that the over-expression of KDX1 up-regulates RCK1 gene expression. To further understand the function of Rck1, microarray analysis was performed using a RCK1 over-expressing strain. Based on microarray and Northern blot analyses, we determined that the expression of KDX1 was downregulated when RCK1 was over-expressed. Furthermore, we determined that phosphorylated forms of Slt2 and Mkk2 were down-regulated by the over-expression of RCK1. Ptp2, a phosphatase that is regulated by the Slt2 MAP kinase pathway, was down-regulated by the over-expression of RCK1. Ptp2 is a negative regulator of Hog1; thus, the phosphorylated form of Hog1 was up-regulated by RCK1 overexpression. A point mutation of lysine 152 to arginine resulted in a failure to up-regulate Hog1 and the subsequent down-regulation of CTT1, which is a Hog1 pathway target gene. Furthermore, using microarray and Northern blot analyses, we determined that genes that are regulated by Msn2/Msn4 were up-regulated by Rck1 and that this was the result of Hog1 activation by RCK1 over-expression. Together, our results suggest that Rck1 inhibits Slt2 MAP kinase pathway activity and then Ptp2, which subsequently activates Hog1. (C) 2013 Elsevier Inc. All rights reserved.