A sequence fragment from the murine Hsp70-1 locus encompassing 655 bp of the 5' flanking and noncoding sequence was adjoined to sequence encoding cre recombinase. Lines 1, 6 and 7 were generated. The pound symbol (#) is used when no line is given and/or lines are pooled. Transgene expression occurred early in embryogenesis, resulting in the production of progeny exhibiting complete recombination of reporter constructs.