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Activation of a Mitogen-activated Protein Kinase,
KFR1, in the Bloodstream Form of Trypanosoma brucei
(Received for publication, August 27, 1996, and in revised form, December 30, 1996)
From the Department of Pharmaceutical Chemistry, University of
California, San Francisco, California 94143-0446
KFR1, a mitogen-activated protein (MAP) kinase
identified in the African trypanosome, Trypanosoma brucei,
is a serine protein kinase capable of phosphorylating the serine
residues in histone H-1, myelin basic protein, and
-casein. It
phosphorylates four proteins with estimated molecular masses of 22, 34, 46, and 90 kDa from the T. brucei bloodstream-form lysate
in vitro. KFR1 bears significant sequence similarity to the
yeast MAP kinases KSS1 and FUS3 but cannot functionally complement the
kss1/fus3 yeast mutant. It is encoded by a single-copy gene
in the diploid T. brucei, and only one of the two alleles
can be successfully disrupted, suggesting an essential function of
KFR1 in T. brucei. KFR1 activity is present at
a much enhanced level in the bloodstream form of T. brucei
when compared with that in the insect (procyclic) form. This enhanced
activity can be eliminated in vitro by the treatment with
protein phosphatase HVH2 known to act specifically on MAP kinases. It
can also be decreased in the bloodstream form of T. brucei
by serum starvation but induced specifically by interferon-
. The
production of interferon-
in the mammalian host is known to be
triggered by T. brucei infection, and this cytokine, as has
been reported, promotes the proliferation of T. brucei in the mammalian blood. Since none of these phenomena can be observed in
the procyclic form of T. brucei, activation of KFR1 is most likely involved in mediating the interferon-
-induced proliferation of T. brucei in the mammalian host.
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