cis-Acting elements of a typical retroviral vector.

Sequences necessary for propagation of a retroviral construct are shown. All viral protein sequences have been deleted and replaced with a foreign gene, which could be a marker gene or another gene of interest. The foreign gene can be expressed from the promoter in the retroviral LTR, as is shown, or from an internal, heterologous viral promoter, as is the usual case with lentiviral vectors, engineered to be part of the vector. Roles of the various sites labeled and of additional cis-acting sequences contained on lentiviral vectors are discussed in the text.