Exons 1 and 2 were replaced with a cassette containing lacZ followed by floxed neo. The deleted sequence encodes 360 N-terminal residues which make up the octapeptide (Eh1 domain), alpha-helix 1, and approximately half of alpha-helix 2 homeodomain. Normal transcript was undetected by in situ hybridization of neural tube sections obtained from hemizygous fetuses. LacZ expression was detected. (J:86206)