1 µl of total RNA was reverse transcribed in an RT mixture containing 50 mM Tris-HCl (pH 8.3), 75 mM KCl, 10 mM dithiothreitol, 3 mM MgCl 2 , 0.5 mM deoxynucleotide triphosphates (dNTPs), 200 U M-MLV reverse transcriptase (Gibco, Gaithersburg, MD), 2 U µl -1 RNase inhibitor (Takara, Shiga, Japan), and 2.5 µM random hexamer (Takara) in a total volume of 20 µl at 42˚C for 60 min.