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J. Virol., Jul 1995, 4112-4121, Vol 69, No. 7
MA Goldsmith, MT Warmerdam, RE Atchison, MD Miller and WC Greene
Recent evidence indicates that the nef gene of human immunodeficiency virus
type 1 augments rather than inhibits viral replication in both cell culture
and in vivo models. In addition, nef alters various normal cellular
processes, including the display of CD4 on the cell surface. However, it
remains unknown whether the enhancement of infectivity and the
downregulation of CD4 represent linked or independent biologic properties
of this single protein. In the present studies, mutational analyses were
performed to define structure-function relationships within the Nef protein
that mediate these effects. To assess the functional consequences of these
mutations, sensitive and reliable assays were developed to quantitate the
viral infectivity enhancement and CD4 downregulation functions of Nef. The
results indicate that membrane-targeting sequences at the N terminus of Nef
are important for both functions of Nef, while certain other conserved
regions are dispensable for both functions. A conserved proline-X-X repeat
segment in the central core of the protein, which is reminiscent of an SH3-
binding domain, is critical for the enhancement of infectivity function but
is dispensable for CD4 downregulation. However, the downregulation of CD4
by Nef appears to involve a two-step process requiring the initial
dissociation of p56lck from CD4 to permit engagement of the endocytic
apparatus by CD4. Together, these findings demonstrate that the infectivity
enhancement and CD4 downregulation activities of human immunodeficiency
virus type 1 Nef can be dissociated. Thus, these processes may be
independent of one another in the viral replication cycle.
Copyright © 1995, American Society for Microbiology
Dissociation of the CD4 downregulation and viral infectivity enhancement functions of human immunodeficiency virus type 1 Nef
Gladstone Institute of Virology and Immunology, School of Medicine, University of California San Francisco 94141, USA.
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