The DNA-binding domain, the hinge domain, and part of the ligand-binding domain (amino acids 25-309) encoded by exons 3-6 were replaced with a PGK-neo cassette via homologous recombination. Northern blot analysis of liver, thymus, and kidney tissue using a probe spanning exons 3-6 confirmed the absence of the targeted region in homozygous mutant animals. When analyzed using a full-length Rorc probe 2 species of mutant transcripts, probably due to alternative splicing events, were detected in homozygous mutants.