Abstract

To investigate the influences of viral infection on cell cycle of marine algae, we examined the changes of expression and activity of G₂/M-phase cell cycle regulators in two unicellular marine algae Emiliania huxleyi and Chrysochromulina ericina after viral infection by immunoblot. The results revealed that the expression of cyclins could be altered by viral infection, thus inhibiting the progression of cell cycle. E. huxleyi virus (EhV) repressed the activity of p34cdc2/cyclinB complex by inactivating p34cdc2 kinase through phosphorylation of Cdc2, and block the life cycle of host cells at G₂/M checkpoint. C. ericina virus (CeV) interfere with the activity of p34cdc2/cyclin B complex by the downregulation of cyclinB combined with the overexpression of kinase-active p34cdc2, resulting in a G₂ cell cycle. The G₂/M cell cycle arrest caused by EhV infection indicated that EhV may transcribe its own genes without relying on the host cell cycle control. C. ericina cells blocked in a delayed G₂ phase may partly turn into the second S phase to synthesize proteins useful for viral nucleic acid metabolism, suggesting that the replication of CeV viruses was dependent on cell cycle control. Our results indicated that algal virus infection selectively activates/inactivates certain components of the cell cycle with the aim to establish a more efficient environment for their gene expression and DNA replication.

Key words: Marine algal virus, cyclins expression, cell cycle arrest.