Three-dimensional structure of the Chinese Sacbrood bee virus

The RNA of Chinese Sacbrood Bee Virus (CSBV) was purified and used as template to obtain a 1096 bp cDNA fragment by RT-PCR amplification. This DNA fragment was cloned into pGEM-T Easy Vector for sequencing. Analyses of the sequenced CSBV RNA fragment revealed a nucleotide sequence homology of 87.6% and a deduced amino-acid sequence homology of 94.6% with that of the Sacbrood Virus (SBV), indicating that CSBV is a different but highly homologous virus of SBV. The three-dimensional (3D) structure of CSBV was determined at 2.5 nm resolution by using electron cryo-microscopy (cryoEM) and computer reconstruction methods. The 3-D structure showed that the capsid has a T= 1 (or P= 3) icosahedral capsid shell with a smooth surface. There were 12 pentons at its icosahedral vertices (5-fold axes) and 132 holes penetrating the shell. The 3-D structure also revealed densities corresponding to the CSBV genome, suggesting icosahedrally-ordered RNA organization, a novel feature not previously reported for any picornavi-ruses.