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J. Virol., 01 1997, 405-411, Vol 71, No. 1
Z He, YS He, Y Kim, L Chu, C Ohmstede, KK Biron and DM Coen
The product of the human cytomegalovirus (CMV) UL97 gene, which controls
ganciclovir phosphorylation in virus-infected cells, is homologous to known
protein kinases but diverges from them at a number of positions that are
functionally important. To investigate UL97, we raised an antibody against
it and overexpressed it in baculovirus- infected insect cells. Recombinant
baculovirus expressing full-length UL97 directed the phosphorylation of
ganciclovir in insect cells, which was abolished by a four-codon deletion
that confers ganciclovir resistance to CMV. When incubated with
[gamma-32P]ATP, full-length UL97 was phosphorylated on serine and threonine
residues. Phosphorylation was severely impaired by a point mutation that
alters lysine-355 in a motif that aligns with subdomain II of protein
kinases. However, phosphorylation was impaired much less severely by the
four-codon deletion. A UL97 fusion protein expressed from recombinant
baculovirus was purified to near homogeneity. It too was phosphorylated
upon incubation with [gamma-32P]ATP in vitro. This phosphorylation, which
was abolished by the lysine 355 mutation, was optimal at high NaCl and high
pH. The activity required either Mn2+ or Mg2+, with a preference for Mn2+,
and utilized either ATP or GTP as a phosphate donor, with Kms of 2 and 4
microM, respectively. The phosphorylation rate was first order with protein
concentration, consistent with autophosphorylation. These data strongly
argue that UL97 is a serine/threonine protein kinase that
autophosphorylates and suggest that the four-codon deletion affects its
substrate specificity.
Copyright © 1997, American Society for Microbiology
The human cytomegalovirus UL97 protein is a protein kinase that autophosphorylates on serines and threonines
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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