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Mol. Cell. Biol., Jan 1995, 345-350, Vol 15, No. 1
D Desai, HC Wessling, RP Fisher and DO Morgan
The cyclin-dependent protein kinases (CDKs) are activated by association
with cyclins and by phosphorylation at a conserved threonine residue by the
CDK-activating kinase (CAK). We have studied the binding of various human
CDK and cyclin subunits in vitro, using purified proteins derived from
baculovirus-infected insect cells. We find that most CDK-cyclin complexes
known to exist in human cells (CDC2- cyclin B, CDK2-cyclin A, and
CDK2-cyclin E) form with high affinity in the absence of phosphorylation or
other cellular components. One complex (CDC2-cyclin A) forms with high
affinity only after CAK- mediated phosphorylation of CDC2 at the activating
threonine residue. CDC2 does not bind with high affinity to cyclin E in
vitro, even after phosphorylation of the CDC2 subunit. Thus,
phosphorylation is of varying importance in the formation of high-affinity
CDK-cyclin complexes.
Copyright © 1995, American Society for Microbiology
Effects of phosphorylation by CAK on cyclin binding by CDC2 and CDK2
Department of Physiology, University of California, San Francisco 94143- 0444.
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