sr-Mouse Polypeptide-5 is a single chain recombinant protein produced by fermentation in E. coli. The starting gene is synthesized to be identical to the gene which codes for Immunoglobulin Heavy Chain Variable Region derived from mouse. The parent protein contains a maximum of 249 amino acids which may contain disulfide bonds and/or glycosylation, and consists of the proper sequence of the 20 standard amino acids.