Activation of p70/p85 S6 kinase by a pathway independent of p21ras

A study of the activation of p70 and p85 S6 kinase by a pathway not influenced by p21ras reveals that the activation is stimulated by the sequential activation of the GDP-GTP exchange factor Sos. The p70 and p85 enzymes are two different forms of the same kinase and are essential for mitogenesis. The cells transformed by the activation of this enzyme exhibit increased phosphorylation, which is different from the activities caused by p42 and p44 kinases.