For Western blotting and coimmunoprecipitation (coIP), protein samples must be extracted from tissues. The protocol described in this chapter has been used to extract clock proteins from mammalian tissues as diverse as liver, kidney, and brain. The extraction protocol is mild enough to be used for coIP as well as Western blotting. Simply, clock proteins are extracted from tissues by freezing and thawing, and homogenizing with a handheld homogenizer. This procedure extracts most (>90%) of the clock proteins from mammalian tissues.
