Abstract
A cDNA clone, which represents a species of mRNA that is expressed in growth-stimulated BALB/c-3T3 cells but not in resting cells, was found to encode a protein remarkably similar in sequence to the members of the immunoglobulin superfamily, especially to the extracellular portion of the mouse interleukin 1 receptor. The immunoglobulin superfamily is believed to be involved in cell adhesion and cell-to-cell interaction. The evidence that a member of this family is induced in the course of the initiation of cell proliferation is intriguing.