Nuclei preparation buffer I

0.3 M sucrose

60 mM KCl

15 mM NaCl

5 mM MgCl₂

0.1 mM ethylene glycol-bis N,N,N′,N′-tetra-acetic acid (EGTA)

15 mM Tris-Cl (pH 7.5)

0.5 mM dithiothreitol (DTT)

0.1 mM phenylmethylsulfonyl fluoride (PMSF)

3.6 μg/ml aprotinin (Sigma)

Protease inhibitors, and in particular PMSF, are rather unstable in aqueous solutions. Therefore, PMSF, as well as DTT and aprotinin, should be added as late as possible, just before use.