The virus binds to the cell surface with the help of surface glycoproteins present over the envelope. This interaction leads to change in the configuration of the proteins which allows the fusion of virions to the host cells. The virus releases its content into the cytoplasm and a reverse transcription complex is formed in order to complete the genome replication.

 

32.1 Reverse transcription

The phenomenon of reverse transcription takes place in the reverse transcription complex. Cellular tRNA acts as a primer which binds to the 5' end of the RNA to form negative sense DNA. Polypurine tract (PPT) present on the RNA acts as a primer for the synthesis of positive sense DNA. RNase H enzymatic property of the reverse transcriptase helps in the cleavage of RNA from a RNA-DNA hetroduplex. The DNA formed because of the reverse transcription is called as PROVIRUS . The DNA of the provirus is longer than the parental genomic RNA. The 3' end of the genomic RNA contains unique region called as U3, similarly, 5' end also contains U5 as unique region. The provirus contains an extra U5 along with U3 and similarly extra U3 with U5 (reason for longer length of provirus). The provirus contains U3- Repeat (R)-U5 sequence at both the ends which is also called as long terminal repeats (LTR).