Many metazoan proteins are multi-domain (colored rectangle, Figure 5B ). We tested whether the viral acquired sequences that belong to multi-domain proteins displayed a stronger tendency for a size reduction (see scheme, Figure 5B ). A reduction in length of viral proteins may be a reflection of reducing the number of domains ( Figure 5B, b-c) , shortening the length of the linker sequences ( Figure 5B , a) or even the trimming of the length of the domain itself.