Bone marrow-derived macrophages (BMMs) from Pias1 null mice were treated with IFN-beta (500 U/ml) for 2h. Total RNA was prepared with RNA-STAT60 (TEL-TEST) and purified with the RNeasy kit (Qiagen). Double stranded complementary DNA was synthesized from 20 ug of total RNA according to Affymetrix methodology, and purified with Phase Lock Gels (Eppendorf). Biotin-labeled RNA was synthesized with the BioArray High Yield RNA Transcript Labeling Kit (Enzo). Samples were cleaned, fragmentated and hybridized to murine genome (MGU74Av2) Genechips (Affymetrix) as instructed. GeneChips were stained with phycoerythrin-streptavidin (Molecular Probes) and scanned with a GeneChip scanner (Affymetrix). Data were analyzed with the GeneSpring software.