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J. Virol., 11 1997, 8176-8185, Vol 71, No. 11
EA Fortunato, MH Sommer, K Yoder and DH Spector
The human cytomegalovirus major immediate-early 86-kDa protein (IE2 86)
plays an important role in the trans activation and regulation of HCMV gene
expression. Previously, we demonstrated that IE2 86 contains three regions
(amino acids [aa] 86 to 135, 136 to 290, and 291 to 364) that can
independently bind to in vitro-translated Rb when IE2 86 is produced as a
glutathione S-transferase fusion protein (M. H. Sommer, A. L. Scully, and
D. H. Spector, J. Virol. 68:6223-6231, 1994). In this report, we have
elucidated the regions of Rb involved in binding to IE2 86 and have further
analyzed the functional nature of the interaction between these two
proteins. We find that two domains on Rb, the A/B pocket and the carboxy
terminus, can each independently form a complex with IE2 86. In functional
assays, we demonstrate that IE2 86 and another IE protein, IE1 72, can
counter the enlarged flat cell phenotype, but not the G1/S block, which
results from expression of wild-type Rb in the human osteosarcoma cell line
Saos-2. Mutational analysis reveals that there are two domains on IE2 86
that can independently affect Rb function. One region (aa 241 to 369)
includes the major Rb-binding domain, while the second maps to the amino-
terminal region (aa 1 to 85) common to both IE2 86 and IE1 72. These data
show that Rb and IE2 86 physically and functionally interact with each
other via at least two separate domains and provide further support for the
hypothesis that IE2 86 may exert its pleiotropic effects through the
formation of multimeric protein complexes.
Copyright © 1997, American Society for Microbiology
Identification of domains within the human cytomegalovirus major immediate-early 86-kilodalton protein and the retinoblastoma protein required for physical and functional interaction with each other
Department of Biology, University of California, San Diego, La Jolla 92093-0357, USA.
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