Step1 - A cellular tRNA binds to the primer binding site (PBS) in the RNA genome.

Step2 - Negative sense DNA is synthesized towards 3' end with the help of virus reverse transcriptase.

Step3 - RNase H digests the RNA from RNA-DNA hetroduplex. First jumps of the negative strand DNA occurs towards 5' end.

Step4 - Negative strand DNA continues to elongate and RNase H digest the RNA- DNA hetroduplex till PPT.

Step5 - Synthesis of positive strand DNA begins from PPT towards 5' direction.

Step6 - All the remaining RNA degraded by RNase H.

Step7 - Second jump occurs were positive sense DNA move from 5' end and binds to the 3' end of the negative sense DNA.

Step8 - Synthesis of remaining strand of the DNA completed.

 

32.2 Integration of the provirus

Newly formed provirus associated with viral integrase is then migrated to the nucleus. The migration of the provirus usually occurs at the time of mitosis because of the fragility of the nuclear membrane at the time of cell division. The provirus with integrase is referred as pre-integration complex. Once inside nucleus, the viral integrase cuts the host chromosome and ligates the provirus into the gap. The provirus may express immediately or may be inactive in case of latent infection. When cell starts dividing the provirus is also copied into the daughter cells along with the host chromosome.

 

32.3 Transcription

The transcription of the provirus starts from the LTR sequence with the help of cellular RNA polymerase II. The transcription begins at U3-R junction and terminates at the R-U5 junction. All the transcripts are capped and polyadenylated. Some of these act as mRNA and some as a progeny genome (Fig 32.2). LTR present on the viral genome act as the promoter and other cellular transcription factors help RNA polymerase II to transcribe the RNA. Transcription produces mRNA's similar to that of genomic RNA that are spliced at different locations to form different mRNA subspecies. Without spliced mRNA forms gag and pol, one time spliced to env mRNA, and two times to TAT, REV and NEF mRNA's. During early phase of transcription only double spliced mRNA's are formed which increases the level of TAT, REV and NEF in the cell. TAT acts as transcription enhancer and REV helps in the export of spliced mRNA.

TAT stands for "Trans-Activator of transcription”.

REV stands for "Regulator of Virion Expression".

NEF stands for “Negative Regulatory Factor”.