= Histone H1 kinase assay
A <histone H1 kinase assay> measures <protein kinase> action on supplied <histone H1>, a <protein> <substrate>. When the transferred <phosphate> carries a radioactive <isotope> label, label incorporated into <histone H1> reports catalytic action over the assay interval. It does not count <CDK1> <molecules>, and a crude preparation can contain other <protein kinases> acting on <histone H1>. Attribution therefore needs controls.
A 2010 study prepared human <HeLa> S3 extracts after a <double thymidine block>, using swelling, a <Dounce homogenizer>, <centrifugation>, <dialysis> and concentration. Added recombinant <cyclin B>1 incubated for $20$ minutes.<Quantitative Reconstitution of Mitotic CDK1 Activation in Somatic Cell Extracts by Richard W. Deibler and others>[Deibler and Kirschner (2010), Experimental Procedures, “Tissue Culture, Flow Cytomtery, and Somatic Cell Extract Preparation”; Figure 2A]{ref}
Aliquots received <histone H1> and terminal-$^{32}\mathrm{P}$-labeled <ATP> for a $15$-minute room-<temperature> reaction, stopped with Laemmli buffer. Dried <SDS-PAGE> gels exposed a <phosphorimager> screen; a BioRad Molecular Imager FX quantified labeling. No-added-<cyclin B> activity set the normalization baseline; RO-3306 reduced H1 activity approximately $85\%$. Companion <Western blots> monitored Tyr15 <phosphorylation>, with <actin> <Western blot loading control>.<Quantitative Reconstitution of Mitotic CDK1 Activation in Somatic Cell Extracts by Richard W. Deibler and others>[Deibler and Kirschner (2010), “H1 Kinase Assays”; Results, “A Three-Stage Activation Profile of CDK1 by Cyclin B”, reported Figure S2A inhibitor result; Figure 2B]{ref}
Mixed extracts lose compartment boundaries; inhibitor sensitivity supports a major <CDK1> contribution, with residual signal.<Quantitative Reconstitution of Mitotic CDK1 Activation in Somatic Cell Extracts by Richard W. Deibler and others>[Results, “Establishing a Somatic Cell Extract System for Mitotic Entry”; “A Three-Stage Activation Profile of CDK1 by Cyclin B”]{ref} <Substrate> choice and inhibitor specificity limit attribution. The <cell-cycle hysteresis experiment> supplies a separate history comparison with this kind of <histone H1> readout; its dose thresholds should not be transferred to human <biological cells>.
\Image[/histone-h1-kinase-assay-readout-controls.png]
{title=The <histone H1 kinase assay>: transferred label, controls and distinct <protein> measurements}
{description=Original explanatory workflow of the inspected 2010 assay. The $20$-minute extract incubation and $15$-minute assay reaction are separate intervals. No gel lanes or measured intensities are simulated. The no-added-<cyclin B> baseline and RO-3306 perturbation have different purposes; neither a total-<CDK1> <Western blot> nor a site-specific <phosphorylation> <Western blot> replaces the catalytic readout.}
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