From a collection of 80 cDNAs representing genes that are induced by serum growth factors in quiescent mouse fibroblasts we have characterized a clone, N51, and demonstrated that it codes for a precursor of a secretory protein. N51 mRNA is rapidly induced by serum, including in the presence of cycloheximide, demonstrating that its induction does not require de novo protein synthesis. The mRNA has a short half-life of approximately 10-15 min and is dramatically prolonged in the presence of protein synthesis inhibitors. Purified growth factors such as platelet-derived growth factor and bombesin are strong inducers of N51 expression. However, epidermal growth factor, fibroblast growth factor, and the tumor promoter tetradecanoyl phorbol acetate have a negligible effect. Transcriptional analysis demonstrates that the increase in N51 mRNA levels after serum stimulation is in part due to the activation of gene transcription.