Gene transfer by retroviral vectors.

Vector and cellular interactions are mediated by the viral envelope and cell surface receptors after which the diploid RNA genome is released into the cytoplasm as single-stranded (ss) RNA. Conversion into double-stranded complimentary DNA occurs through action of viral reverse transcriptase leading to formation of a circular double-stranded DNA intermediate as part of the pre-integration complex. This pre-integration complex reaches the nucleus either during mitosis in the case of oncoretroviral vectors or by direct nuclear transmigration in the case of lentiviral vectors. Subsequent integration of the proviral genome into chromosomal DNA is mediated by viral integrase. The long terminal repeats (LTRs) that contain transcriptional control and RNA processing signals, flank the integrated vector encoded genes and modulate their expression.

Abbreviations: LTRs, long terminal repeats