Modified rat matrix metalloproteinase 3 (Mmp3) sequence was adjoined to a 2.4 kb murine Wap promoter fragment. The Mmp3 sequence contained a valine to glycine substitution mutation at codon 92 (see Erratum for J:18003), thereby conferring autoactivation. Immunocytochemical analysis identified abundant transgenic protein in mammary tissues in pregnant and lactating mice. (J:18003)