OGFr protein size polymorphism correlates with the number of 20 amino acid tandem repeats present. (A) Cytoplasmic fractions (20 µg/lane) from the cell lines K008, U937, or peripheral blood lymphocytes from seven normal donors were separated on an 8% acrylamide gel, transferred to nitrocellulose, and probed with an antibody to the OGFr tandem repeat region. (B) The R_f of the proteins correlates with the number of tandem repeats (TRs) contained in the protein using K008 (6.8 repeats) and U937 (4.8 repeats) as known points, and suggest that the size heterogeneity occurs in discrete 20 amino acid increments.