Which type of virus can be read directly for the synthesis of viral proteins?

Positive-sense single-stranded RNA viruses contain their genetic material in a form that can be directly translated into proteins by the host's ribosomes. This means that once the virus enters the host cell, its RNA can essentially be read by the cellular machinery to synthesize the viral proteins immediately. This characteristic allows for rapid replication and protein production, which is crucial for the virus's life cycle.

In contrast, double-stranded RNA viruses must first convert their RNA into a usable form before protein synthesis can occur. Negative-sense single-stranded RNA viruses require a complementary positive-sense strand to be synthesized first, which then acts as a template for protein production. Retroviruses, while they do convert RNA into DNA within the host cell, still need to undergo additional steps before the host can synthesize viral proteins. Thus, the ability of positive-sense single-stranded RNA viruses to be directly translated into proteins distinguishes them from the other types listed.