A targeting vector was assembled by Red/ET recombination in which cre recombinase was driven by the Sykb regulatory elements. An FRT-flanked Pgk-neomycin selection cassette was included in the construct. The construct was electroporated into R1 ES cells. Correctly recombined clones were injected into C57BL/6 blastocysts to generate chimeras. (J:159112)