A loxP site and an frt flanked neo resistance cassette were inserted in intron 3. At the same time, an additional loxP site was inserted in intron 6a. Correctly targeted mice were crossed to Gt(ROSA)26Sor mice to excise the selection cassette. These mice were then bred to an unspecified EIIa-cre transgenic mouse to delete exons 4 through 6a. Immunoblot analysis confirmed the absence of protein product. (J:141583)