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J. Virol., Jan 1998, 558-563, Vol 72, No. 1
X Cullere, P Rose, U Thathamangalam, A Chatterjee, KP Mullane, DC Pallas, TL Benjamin, TM Roberts and BS Schaffhausen
Polyomavirus middle T antigen (MT) is phosphorylated on serine residues.
Partial proteolytic mapping and Edman degradation identified serine 257 as
a major site of phosphorylation. This was confirmed by site-directed
mutagenesis. Isoelectric focusing of immunoprecipitated MT from transfected
293T cells showed that phosphorylation on wild-type MT occurred at near
molar stoichiometry at S257. MT was previously shown to be associated with
14-3-3 proteins, which have been connected to cell cycle regulation and
signaling. The association of 14-3-3 proteins with MT depended on the
serine 257 phosphorylation site. This has been demonstrated by comparing
wild-type and S257A mutant MTs expressed with transfected 293T cells or
with Sf9 cells infected with recombinant baculoviruses. The 257 site is not
critical for transformation of fibroblasts in vitro, since S257A and S257C
mutant MTs retained the ability to form foci or colonies in agar. The tumor
profile of a virus expressing S257C MT showed a striking deficiency in the
induction of salivary gland tumors. The basis for this defect is uncertain.
However, differences in activity for the wild type and mutant MT lacking
the 14-3-3 binding site have been observed in transient reporter assays.
Copyright © 1998, American Society for Microbiology
Serine 257 phosphorylation regulates association of polyomavirus middle T antigen with 14-3-3 proteins
Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
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