A floxed neomycin resistance gene was inserted in intron 8 and another loxP site was placed in intron 7. Also, frt sites were inserted on either side of exon 9. Transient cre expression in the ES cells removed exon 8 which caused a frame shift and a premature termination codon in exon 9. RT-PCR indicated mRNA of 510bp rather than 623bp. There was also a minor smaller transcript of 291bp. No protein product could be seen immunologically in skin biopsies of homozygous mice. (J:85981)