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For a retrovirus to replicate, it needs a surface coating of the 'envelope' or 'env' protein. This allows the virus to attach itself to its target cell type and assists in inserting its payload into the target cell.

The payload, wrapped in its own special proteins, is inserted into the target cell. The payload consists of the virus' own RNA, plus reverse transcriptase, and a protein called integrase.

The protein coat is digested away. Then the reverse transcriptase 'reads' the viral RNA and constructs a DNA version using host cell resources (host cell DNA nucleotides). The DNA version is called a precursor virus or provirus.

Integrase then attaches to the viral DNA provirus and to the host DNA, snipping the host DNA and inserting the provirus, aided by sections of viral DNA known as long terminal repeats (LTRs).

The video illustrates the operation of the HIV retrovirus. All retroviruses operate in basically the same way.

A note of caution! Although these sorts of videos are great for getting an idea of molecular biological processes, it is easy to get an impression of orderliness and purpose which is not there in reality. Molecules do not glide towards specific targets as if they know what they are doing! The reality is that there is a blizzard of activity of all sorts, with all sorts of molecules blindly milling around. In these animations, only the significant and relevant interactions are being depicted.

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