Structure of mouse protein S as determined by PCR amplification and DNA sequencing of cDNA

The cDNA sequence of mouse protein S was derived by conventional PCR amplification from liver mRNA, initially using primers derived from the human cDNA sequence, followed by direct DNA sequencing. Seven overlapping PCR fragments covering all of the mature protein, part of the propeptide, and the 3' noncoding region were generated and sequenced. In some cases primers based upon the human cDNA sequence were ineffective. Subsequent successful amplification with mouse-derived primers to the same regions and comparison of the mouse and human sequences in these regions suggest that the failure of the human primers was due to insufficient degree of heterospecies identity. The mouse protein S cDNA sequence of the coding region shares 82% identity to human. The 3' noncoding region of mouse protein S cDNA has several small deletions and insertions compared to human protein S cDNA. Mature mouse protein S consists of 634 amino acids in a single polypeptide chain and displays domain organization similar to that for other species. The amino acid sequence of mouse protein S is about 80% identical to that of other species. Eleven glutamic acid residues were found in the amino terminal region and are predicted to be sites of gamma-carboxylation. Amino acid residues #80-244 are defined as four cysteine-rich repeat sequences homologous to epidermal growth factor. The remainder of the molecule is homologous to plasma sex steroid binding protein. The mouse protein S contains two potential N-glycosylation sites at positions #458 and 468 and is lacking the putative glycosylation site at #490 found in human protein S.