Biology Reference
In-Depth Information
Fig. 11.1 Progression through the cell division cycle is controlled by the activities of specific
CDK-cyclin complexes at each phase
progression is believed to be driven primarily by combinations of these CDKs and
their cyclin partners.
Cyclins are a diverse family of proteins, all of which contain a stretch of 150
amino acids termed the 'cyclin box' (Malumbres and Barbacid
2005
). They were
first identified in marine invertebrates as proteins whose abundance oscillated
during the cell cycle (Evans et al.
1983
). There are at least 29 genes encoding
cyclins in human cells, although not all have known CDK partners (Malumbres
and Barbacid
2005
). Those cyclins that do have known CDK partners and that
regulate progression through the cell cycle fall into four major classes: D, E, A,
and B type cyclins (Satyanarayana and Kaldis
2009
). The D type cyclins bind
CDK4 and CDK6 in G1 phase, the E type cyclins bind CDK2 at the G1-S phase
transition, the A type cyclins bind CDK2 during S phase and CDK1 during G2
phase and the B type cyclins bind CDK1 during the G2-M transition and early
mitosis (Satyanarayana and Kaldis
2009
) (Fig.
11.1
).
11.1.1 Regulation of CDK-Cyclin Activities
The catalytic activities of CDKs are tightly regulated in a strict spatio-temporal
manner by a number of complementary mechanisms, including cyclin binding,
changes in cyclin levels (determined by gene expression and proteolysis), protein
phosphorylation and dephosphorylation, binding to CDK inhibitors, and subcel-
lular localisation (Morgan
1995
; King et al.
1996
; Booher et al.
1989
).
