Overview of the retroviral life cycle. After the virus attaches to a cell surface receptor, the viral core containing two complete genomic RNAs enters the cytoplasm. Reverse transcription of the viral RNA occurs within the nucleoprotein complex of the core in two steps. First, reverse transcriptase (RT) copies the viral RNA into a single-stranded minus-strand DNA by RNA-dependent DNA synthesis. Next, RT copies the minus-strand DNA into the double-stranded DNA by DNA-dependent DNA synthesis. The viral DNA enters the nucleus and integrates at random positions into the host cell chromosome to form a provirus. The viral DNA may be amenable to mismatch repair either before or after integration, but before cell division. Host cell DNA polymerases replicate the integrated provirus through each cell division and chromosomal replication. The host cell RNA polymerase II transcribes the provirus to form RNA that can serve as genomic RNA or as mRNA for translation of viral proteins. Progeny viruses assemble at the plasma membrane. The polymerization steps in the viral life cycle that can introduce mutations into the viral genome, and host cell mismatch repair enzymes that may correct the mutations, are labeled in boldface letters.
