Three-dimensional reconstruction of hibiscus chlorotic ringspot virus.

Hibiscus chlorotic ringspot virus (HCRSV) is a positive-sense, single-stranded RNA virus, which belongs to the Tombusviridae family and infects plants of the Hibiscus genus, including kenaf, a woody plant of agricultural importance. These icosahedral viruses have a capsid consisting of 180 copies of coat protein (CP) arranged with T=3 symmetry. The CP consists of an internal RNA-binding domain, a shell-forming domain and a protruding domain. The HCRSV virion was reconstructed to about 12A resolution from cryo-EM images using the program EMAN. The structure had the arrangement of 90 dimers of protruding domains characteristic of the Tombusviridae. Reconstructions were also made from negatively stained samples, and showed essentially the same features. In addition, a particle of a different, "smooth" appearance was also identified in the negatively stained samples. These particles were slightly smaller and lacked protruding domains. Biochemical analysis confirmed the presence of two protein products: a 37 kDa protein identified as HCRSV CP and a 54 kDa protein that appeared to be of non-HCRSV origin.