Complete genome of Chinese sacbrood virus from Apis cerana and analysis of the 3C-like cysteine protease.

The complete genome sequence of Chinese sacbrood virus (CSBV), isolated from diseased larvae of Apis cerana in Fujian province, China was analyzed. The viral genome consisted of 8,800 nucleotides, encoding 2,848 amino acids. A phylogenetic tree analysis showed the sacbrood virus (SBV) segregated into three distinct groups. The isolates originated from A. c. indica and were the first distinct evolutionary group. The AcSBV-SBM2 isolate, from A. c. cerana, belonged to the second distinct group. The remaining SBV isolates formed the third group. The phylogenetic relationships of SBV isolates suggest that they are derived from similar honeybee species or geographic origins. The 3C-like cysteine protease protein plays an important role in viral replication. The 3C-like cysteine protease protein of CSBV-FZ was predicted to contain a transmembrane domain. The subcellular localization of 3C-like cysteine protease was distributed as discrete punctate inclusions and co-localized with VP1 of CSBV. These results suggest that the non-structural protein 3C-like cysteine protease might be involved in viral replication. Insect cell cultures can further advance our understanding of picorna-like virus replication.