Immunoprecipitation of the proteins synthesized in the culture medium by adherent cells of mouse long-term bone marrow culture (LTBMC) or cells from 1 week postnatal mouse bone marrow (BM) with an antiserum against laminin-1 (1β1γ1), laminin 1 chain (1; MoAb 198) or with a nonimmune rabbit serum (NRS). Positions of a prestained 200 and 70 kD molecular mass markers and 400 kD laminin 1 polypeptide from EHS extract stained by Coomassie blue after electrophoresis are shown to the left. LTBMC: 6% gel; BM: 3% to 12% gradient gel.