The cDNA and gene coding for mouse hepatocyte growth factor-like protein (HGF-like protein) were isolated and characterized. The size of the gene from the site of initiation of transcription to the polyadenylation site is 4613 bp in length and is composed of 18 exons separated by 17 intervening sequences. The exons range in size from 36 to 227 bp in length, while the intervening sequences range in size from 78 to 613 bp in length. The site of initiation of transcription was identified by primer extension analysis using total RNA isolated from mouse liver. On the basis of these results, the first exon is 146 bp in length and includes 94 bp of 5'-noncoding sequence. The sequence 5'TATGTG3' is present between 34 and 39 bp upstream of the transcription start site and could potentially be the TATA sequence found for many constitutively expressed eukaryotic genes to be the promoter for RNA polymerase II. The sequence 5'GCAAT3' at -96 to -92 may be the CCAAT sequence responsible for stimulation of transcription of some eukaryotic genes. The same sequences in the Genbank and NBRF databases were homologous to similar regions in the genes coding for both human and mouse HGF-like protein (Han et al., 1991). The acyl-peptide hydrolase gene is 410 bp downstream of the mouse HGF-like protein, but is transcribed from the complementary strand. The mouse cDNA for HGF-like protein codes for a putative protein with the same domain structure as its human homologue with four kringle domains followed by a serine protease-like domain. On the basis of the translated sequence of the cDNA, the mouse HGF-like protein would be 716 amino acids in length with a molecular weight of 80K. There are four potential N-linked carbohydrate attachment sites. The DNA and amino acid sequences of mouse HGF-like protein are compared to the human protein. Overall, the two proteins are about 80% identical with each other. In contrast to mRNA for human HGF-like protein, which is 2.4 and 3.0 kilobases in length in human liver, only the smaller species is seen in mouse and rat liver. The expression pattern of mRNA coding for HGF-like protein during development and in maternal rats was determined by Northern analysis. It is apparent that the majority of mRNA coding for HGF-like protein is expressed in liver. Messenger RNA is also expressed at a lower level in lung, adrenal, and placenta.