Cell division is probably the basic process that defines living organisms. This is a basic cellular mechanism that has remained virtually unchanged over millions of years of evolution. In all eukaryotes, the cell cycle is governed by a heterodimeric protein kinase composed of a Cdk subunit and a cyclin subunit. The Cdk have a catalytic site but are not functional without activating cyclin binding. The Cdk are usually present throughout the cycle while the cyclins are synthesized only in certain phases .


Traditionally, therefore, considered that in unicellular organisms was needed just one Cdk (the Cdk1), while in multicellular organisms is required up to five specific Cdk function of the cell cycle phase was developed at that time. This theory was challenged some years ago in a supervised, as in this case, Mariano Barbacid of the National Cancer Research Center. At that time, research conducted found that the Cdk2 was not necessary to complete the S phase and to generate viable mice. In that result, followed by others in the same direction with Cdk4 and Cdk6.


On this occasion, Barbacid collaborators have succeeded in demonstrating that these three Cdk allegedly required to complete phases G1, S and G2 are not required to complete the normal course of cell cycle. It appears that Cdk1 is the only protein essential to complete cell division, while the rest of Cdk are needed just to provide enough specialized cells Cdk kinase activity for the division within a suitable environment in the tissues of organisms multicellular.