by centrifugation and suspended in 100 μl of 1X Reporter lysis buffer (Promega, Madison, WI). Cell extracts were prepared by three repeated cycles of freeze-thawing followed by centrifugation at 16,000 × g for 1 min. Luciferase assays were carried out using 20 μl of the extract and the Luciferase assay system (Promega, Madison, WI). β-galactosidase assays were carried out using 5 μl of the extract and the Galacto-Light System (Tropix, Bedford, MA). Activities were measured on a Lmax Plate Luminometer (Molecular Devices Sunnyvale, CA).
