Antibodies immobilize and destroy their specific antigens. A mouse can make 10,000,000 antibodies, more than the total genes of the mouse would suggest. Antibody proteins are composed of two long and two short chains. Each species has a constant region characteristic for the species and type of antibody. The viruses of eukaryotes are similar to prokaryote-infecting viruses.
Proviruses are viral DNA integrated into the host cell.
SV40 can introduce new functional genes into the host DNA, as can a number of other viruses. Retroviruses can also insert their nucleic acid into host DNA via the reverse transcriptase mode mentioned previously. Reverse transcriptase is carried with the RNA into the host cell. These LTRs may also make insertion of the viral DNA into the host DNA easier. The inserted viral DNA makes RNA transcripts which are packaged with viral protein coats and reverse transcriptase.