This is the same video as on the last page, because we've only discussed half the story. We left the retrovirus in its provirus form, integrated into the host DNA. The second half of the video shows the second half of the story, the production of new viral particles.

As part of the normal operation of the cell, a molecule called RNA polymerase 'reads' sections of DNA, and produces strands of 'messenger' RNA (mRNA). When these strands meet other molecules called ribosomes, the messenger RNA is translated into proteins.

When the retrovirus' genes are read and converted into proteins, all the proteins required to reconstruct the original virus are produced. The genes include those for the the group antigens (called 'gag'), which make up the infrastructure of the virus particle, the gene for the reverse transcriptase (called 'pol'), and the gene for the environment protein (called 'env'). A string of untranslated RNA is also produced, which makes up the genome of the virus in RNA form.

It is important to note that the integrated provirus consists of DNA that specifies all the proteins required to reconstruct new retroviral particles. This typically consists of around 10,000 base pairs, all of it dedicated to the production of new viral particles.

When we see a length of DNA starting and ending with LTRs, containing gag, pol and env, we can recognise the signature of a retrovirus.