English: The T=1 inner capsid encloses the 10 double-stranded RNA gene segments and is covered by a T=13 outer capsid. Twelve spikes project from the core through the outer capsid. Gene segments are classified as large (L), medium (M), or small (S) based on relative electrophoretic mobilities. Viral capsid proteins are labeled. Nine of the 10 reovirus gene segments code for a single protein; the exception is the S1 gene, which codes for both the (sigma)1 attachment protein and the (sigma)1s nonstructural protein in overlapping reading frames. Viral proteins are named with the Greek letters (lambda), (mu), and (sigma), corresponding to the size classes (L, M, and S) of their respective gene segments.