An 8.3 kb fragment of the mouse insulin promoter (Ins1; from nucleotide -8280 to +12 relative to the transcriptional start site) drives cDNA encoding cre recombinase fused to the mutated mouse estrogen receptor ligand-binding domain. A 2.1 kb fragment of the hGH gene was added to function as a transcriptional stop signal. The 12.5 kb construct was purified and microinjected into fertilized pronuclei of CD1 mice. Line 1 was established. (J:169727)