By specialized viral nucleic acid-binding proteins . The genome is associated with specialized nucleic acid binding proteins. The exact nucleoprotein structure formed by these proteins with the nucleic acids are not known. By cellular DNA binding proteins . The circular, double-stranded DNA genomes of these viruses are coiled around cellular nucleosomes containing the four core histones H2A, H2B, H3, and H4.
Some viruses have an additional outside layer or envelope.
The envelope consists of a lipid layer derived from the infected cell and viral membrane proteins. Membrane proteins all have a transmembrane anchor domain and may be further modified by addition of carbohydrates, phosphorylation, disulfide bonds to other viral proteins, etc. A virus is a an example of viral membrane glycoprotein found on the envelope. Alternatively the envelope can consist of additional protein layers that mediate interaction of the innermost, genome-containing structure with viral envelope. Many viruses acquires this envelope by a process known as budding.