New targets for viral cyclins.

It is now clear that viral cyclins have new functions that provide infected cells with additional stimuli that further activate cell cycle progression. These proteins resist the actions of cell cycle inhibitors, extend the range of cdk substrates, and as a consequence favor cell proliferation and virus propagation. Like some of the endogeneous cyclins, these viral proteins might have also important functions during transcriptional regulation. Binding to transcriptional regulator might enable the virus to target multiple functions of transcriptional activation and cell growth. Whether these effects have any physiological relevance during viral replication or cell transformation will be an important issue to address.