Specific inhibitors of metalloproteinases, such as TIMP, are potential regulators of tissue integrity. In order to understand their exact role in both normal and pathological processes we have initiated molecular studies on the TIMP gene and its product(s). We have used cDNA and genomic clones corresponding to the murine TIMP gene to define the intron-exon structure of the gene and to map multiple clustered sites where transcription is initiated; we have also partially characterized the cis-acting DNA sequences required for transcriptional activity. The murine TIMP cDNA has also been used in transcription/translation experiments to produce polypeptides which can be processed by endoplasmic reticulum membranes and which are biochemically active in inhibition of fibroblast interstitial collagenase. As a result of our analysis of the expression of the TIMP gene in different cell types and under varied conditions, we have observed an important increase of TIMP mRNA levels in mouse fibroblasts in response to physiological modulators (whole serum and double-stranded RNA) as well as a pathogen (NewCastle Disease Virus). In addition, an analysis of TIMP mRNA in several variants of a cell line derived from a spontaneous mammary adenocarcinoma, which possess different levels of metastatic potential indicated that the serum dependence of TIMP mRNA accumulation is different in metastatic as compared to nonmetastatic cells. The significance of these results in view of the role of TIMP in matrix maintenance is discussed.