Viral cyclins

Cyclins are regulatory subunits of the cyclin-dependent protein kinases (CD Ks). Members of this serine-threonine kinase family regulate the progressio n of cells through the division cycle. Until some years ago, cyclins were p resumed to be encoded exclusively by eukaryotic cells. However, sequencing in 1996 of a simian herpesvirus, the herpesvirus saimiri, uncovered an open reading frame with sequence similarity to cellular cyclins. What at the ti me was a surprise for virologists and cell biologists alike, has become an accepted occurrence now. Eight different cyclin-encoding viruses have been described to date. One of them is the recently discovered human herpesvirus 8 (KSHV) suspected to cause Kaposi's sarcoma and certain B cell-lymphoprol iferations in man. The significance of virus-encoded cyclins in the viral l ife cycle is currently unclear. However, the link between specific cellular cyclins and cancer suggests that virus-encoded cyclins could be involved i n oncogenic events associated with these cyclin-encoding viruses. Copyright (C) 2000 John Wiley & Sons, Ltd.