This vector was designed for assembling gene targeting constructs using the BAC recombineering approach. The vector contains a puromycin-(delta)thymidine kinase fusion gene driven by the mouse phosphoglycerol kinase promoter (pUDTK) and a neomycin resistant gene driven by the bacterial EM7 promoter (EM7neo). These selectable markers are flanked by lox66 and lox2272 sites (Cre-recombinase recognition sequences) in a pBluescript KS+ backbone with a modified multi-cloning region