Nuclear localizing Cre recombinase is expressed under control of a 5.4-kb genomic DNA fragment containing the Hes7 (hairy and enhancer of split 7 (Drosophila)) promoter. Cre mRNA is expressed in the presomitic mesoderm (PSM) of the E10.5 embryo, and its expression appears to oscillate. In doubly transgenic embryos bearing this transgene and a lacZ reporter transgene, X-gal staining is observed throughout the PSM and in the somites and their derivatives at E7.5-E10.5. (J:124102)