A cDNA was cloned from a pregnant mouse uterus cDNA library. On conceptual translation, the cDNA has one long open reading frame that predicts a novel protein of 606 amino acids. This protein is principally composed of two CUB domains and a ZP domain; motifs found in proteins implicated in egg-sperm recognition. Probes derived from the cDNA were used to conduct Northern hybridizations. The expression of this mRNA is temporal; message first appears in the uterus 6 days prior to birth, it increases each subsequent day to attain maximal levels at 3 days prior to birth and then abruptly decreases during the last 3 days of pregnancy. The expression of this mRNA is restricted; message is abundant in the uterus during late pregnancy, but it is not found in non-pregnant uterus or in a variety of adult or fetal tissues. The temporo-spatial expression of this pregnant uterus specific mRNA and the consolidation in the predicted protein of two motifs implicated in early pregnancy events suggests that the product of the gene represented by this mRNA may play an important role in events that transpire during late pregnancy.