| Abstract | In eukaryotes, cyclin-dependent protein kinases interact with cyclins to regulate cell cycle
progression, and are required for the G1 and G2 stages of cell division [ 3322810]. The
proteins bind to a regulatory subunit, cyclin-dependent kinase regulatory subunit (CKS),
which is essential for their function. This regulatory subunit is a small protein of 79 to 150
residues. In yeast (gene CKS1) and in fission yeast (gene suc1) a single isoform is known,
while mammals have two highly related isoforms. The regulatory subunits exist as hexamers,
formed by the symmetrical assembly of 3 interlocked homodimers, creating an unusual
12-stranded beta-barrel structure [ 8211159]. Through the barrel centre runs a 12A diameter
tunnel, lined by 6 exposed helix pairs [ 8491379]. Six kinase units can be modelled to bind the
hexameric structure, which may thus act as a hub for cyclin-dependent protein kinase
multimerisation [ 8491379, 8211159].
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