Target silencing by siRNA. (A) WEE1 and CHEK1 transcript levels after treatment with siRNA targeting WEE1 or CHEK1 compared with NS-siRNA. (B) Immunoblots of extracts from cells treated with WEE1 or CHEK1 siRNA with and without 270nM Ara-C. WEE1 (top panel) and CHEK1 (bottom panel). NS indicates the nonsilencing control; and UT, untreated control.