It has been demonstrated that a glucosamine-containing macromolecular component of the cell surface of 3T3 mouse cells, and SV40-transformed cells, is released from cells by treatment with trypsin under conditions in which the plasma membrane remains functionally intact. This was shown by the fact that the treated cells could be cloned with high plating efficiency and remained impermeable to the vital stain, erythrocin. A method for specifically marking this surface component has been devised based on the finding that in 3T3 cells growing synchronously after subculture by trypsin maximum incorporation of glucosamine into this material occurs 12-13 h thereafter. Of the total radioactive glucosamine incorporated into macro-molecular cell constituents, over 80% was recovered in surface component.
Studies on the biosynthesis of surface component revealed that this was periodic during a cycle of cell duplication, with an increased rate of formation immediately after cell division. It was found that the surface component of 3T3 cells differed from that of SV40-transformed cells.
Cryoelectron Microscopy of Mouse Mammary Tumor Virus