Northern blot analysis of Ft subunits and TfR mRNA content of LY cells. Ten micrograms of total cellular RNA were electrophoresed on a formaldehyde-agarose gel (1%) and transferred to a nylon membrane. The membrane was hybridized with³²P-labeled H-Ft, L-Ft, and TfR cDNA probes as described in “Materials and methods.” The mouse GAPDH probe was used as a control for RNA loading. Data shown are representative of 3 to 5 analyses of RNA samples isolated from cells from separate cultures.