ABSTRACT
MicroRNAs (miRNAs) are small (approximately 22 nt) RNAs that exhibit a diversity in sequence,structure,abudance,and expression profile. Bioinformatic approaches and direct cloning methods have identified 3518 miRNAs from various species. MiRNAs play a pivotal role in the regulation of genes involved in diverse processes such as development,differentiation,and cellular growth control. Recently,many viral-encoded miRNAs have been discovered, most from the herpesviruses viral family. Virus-encoded miRNAs seem to evolve rapidly and regulate both the viral life cycle and the interaction between viruses and their hosts. The detailed study on the virus-encoded microRNAs and the role they play in the progress of viral infection,replication and expression will be beneficial to understand viral molecular biology,and also provide new strategies for the prevention and treatment of virus.