E2F is a mammalian transcription factor that appears to play an important role in cell cycle regulation.While at least two proteins (E2F-1 and DP-1) with E2F-like

The envelope glycoprotein gp120 of primate immunodeficiency viruses initiates viral attachment to CD4' cells by binding to the CD4 antigen on host cell surfaces.

E2F is a mammalian transcription factor that appears to play an important role in cell cycle control. DNA

Recent evidence indicates that primary clinical isolates of human immunodeficiency virus type 1 (HIV-1) require significantly more soluble CD4 (sCD4) to block infection than the prototypic laboratory strain HTLV-IIIB. The currently accepted explanation for these observations is that the envelope glycoproteins from primary clinical isolates possess lower affinities for CD4 than laboratory strains. This observation has far reaching implications for the clinical effectiveness of sCD4. To test whether the resistance of clinical isolates to sCD4 neutralization correlates with low-affinity binding to gpl20, we have compared gpl20 glycoproteins derived from the clinical isolates HIV-1 JR-CSF and JR-FL with those derived from the prototypic strain HIV-1 BH10 in quantitative sCD4 binding studies. Surprisingly, our results demonstrate that gpl20 derived from HIV-1 JR-CSF and JR-FL possess sCD4 binding affinities of equal or greater magnitude than gpl20 derived from HIV-i BH10. Thus primary clinical HIV-1 isolates can and do possess gpl20 with high affinity for CD4, and sensitivity to neutralization by sCD4 is dependent upon factors other than the intrinsic affinity of gpl20 for CD4.

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