Phosphorylation of p70S6K and p85S6K on Thr389 in normal melanocytes and NZM cell lines. The higher molecular weight p85S6K and lower molecular weight p70S6K is indicated by arrows. Western blots representative of three independent experiments. Western blots are separated into boxes representing each NZM cell line for clarity. Cells were grown in the absence of FBS for 16 hours (SS) or in the presence of FBS (Ser).