Integration of the viral Genome into Cellular DNA

The double-stranded linear DNA molecule produced by reverse transcription is made circular and inserted in random sites in the cell’s genome, using a polproduct, integrase protein. This protein recognizes sequences at the ends of the DNA of the long terminal repeats (LTRs) to direct linear integration of the DNA provirus, in such a way that the provirus is always joined to host DNA 2 bp from the ends of the LTRs. The DNA copy of the genome now has two identical repeats at either end of the gag-$ol-env regions, known as the LTRS. Each LTR consists of a U3-R-U5 cassette and represents the intact regulatory region, including all the transcriptional sequences necessary

to allow expression of the viral DNA genome (Fig. 3).