Effect of constitutively active 4EBP-1 on p27Kip1 and cyclin D1 mRNA levels. (A) MCF7-4EBP-1-5A cells were cultured with or without pon A for 2 days and then the levels of mRNA encoding p27Kip1 (top panel) or cyclin D1 (middle panel) were determined by Northern blotting. Total RNA was detected by staining the gel with Sybr Gold prior to transfer (bottom panel). (B) Densitometric quantitation of the Northern blot data shown in A. White bars denote RNA levels in the absence of pon A and black bars denote synthesis in the presence of pon A.