RACK1 (receptor for activated C kinase 1) is a 317 amino acid G protein b subunit-like protein that functions as a RACK and inhibits the activity of Src tyrosine kinases. In response to PKC activation, the intracellular localization of RACK1 and PKC bII changes, and RACK1 and PKC bII co-localize to the same sites. RACK1 is therefore thought to be a shuttling protein for PKC bII. A deficit in RACK1 may be associated with impaired PKC activation in the aging brain.