Nuclei labeling buffer

20 mM Tris-Cl (pH 8.0 at 4°C)

140 mM KCl

1 mM MoCl₂

20% (v/v) glycerol

10 mM MgCl₂

10 mM phosphocreatine

100 µg/ml phosphocreatine kinase

0.1 µM [³²P]UTP, 500-5000 µCi/ml

14 mM β-mercaptoethanol

1 mM each of ATP, GTP, and CTP

Just before use, add the last five ingredients and keep the solution at 4°C. Exercise extreme care after the radioactive UTP has been added.