The particles are roughly spherical, and about 100nm diameter. They have several hundred knobbed spikes. The nucleocapsid protein is helical and not noticeable by em.
An obvious outer layer of capsid protein is icosahedral or cone-shaped, depending on genus. This comprises the bulk of the virus and is termed p27 or30 (its MW in Kd).
The RNA genome has 3 genes, gag, pol and env.
Gag (group-specific antigen coding gene) encodes the capsid proteins and the proteases which cleave them and the envelope spikes;
pol encodes the reverse transcriptase enzyme; and the integrase (see later);
env encodes the envelope spikes whose knob is termed gp 69 or 70.