EN
<Mitotic cyclins> constitute a regulatory subunit of the <histone H1 kinase> complex. On the ground of their primary structure they are divided into two classes A and B, both necessary for the <mitosis>. <Cyclin A> activates histone H1 kinase and becomes destroyed by <proteolysis> earlier than <cyclines B> and plays an important role in the <DNA replication>. <Cyclins> A and B may be involvent in the development of <neoplastic disorders> either directly inappropriate expression of the cyclin A gene caused by hepatitis B virus in hepatocellular carcinoma, or interactions of this cyclin with factors paricipating in the regulation of cell proliferation or indirectly by phosphorylation of some oncogene or antioncogene proteins by a cdk (cyclin dependent kinase).