Cheryl K. Lapham, ^* Jun Ouyang, Bhaskar Chandrasekhar, Nga Y. Nguyen, Dimiter S. Dimitrov, Hana Golding

Accessory cell-surface molecules involved in the entry of human immunodeficiency virus-type 1 into cells have recently been identified and shown to belong to the family of chemokine receptors. Treatment of human cell lines with soluble monomeric gp120 at 37°C induced an association between the surface CD4-gp120 complex and a 45-kilodalton protein, which can be down-modulated by the phorbol ester phorbol 12-myristate 13-acetate. The three proteins were coprecipitated from the cell membranes with antibodies to CD4 or to gp120. The 45-kilodalton protein comigrated with fusin on sodium dodecyl sulfate gels and reacted with rabbit antisera to fusin in protein immunoblots. No 45-kilodalton protein could be coprecipitated from similarly treated nonhuman cells. However, infection of 3T3.CD4.401 cells with vaccinia-fusin recombinant virus (vCBYF1), followed by gp120 treatment, resulted in coprecipitation of fusin and CD4.401 molecules from their membranes. Together these data provide evidence for physical association between fusin and the CD4-gp120 complex on cell membranes.

C. K. Lapham and H. Golding, Division of Viral Products, Center for Biologics Evaluation and Research (CBER), Food and Drug Administration, Building 29B, Room 3G21, HFM 454, 8800 Rockville Pike, Bethesda, MD 20892, USA.
J. Ouyang and D. S. Dimitrov, Section on Membrane Structure and Function, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
B. Chandrasekhar and N. Y. Nguyen, Facility for Biotechnology Resources, CBER, Food and Drug Administration, Bethesda, MD 20892, USA.
^*   To whom correspondence should be addressed.