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. 2015 Dec 29;27(3):255–266. doi: 10.1089/hum.2015.110

Figure 1.

Figure 1.

Insulated foamy viral (FV) vectors. (a) Candidate insulators. The 650cHS4 insulator is derived from the 1.2-kbp chicken hypersensitivity site 4 (cHS4) from the chicken β-globin locus. This insulator contains the 5′-most 250-bp core containing the CCCTC-binding factor (CTCF)-binding domain and the terminal 400-bp portion. The 6xCTCF insulator contains alternating repeats of the CTCF-binding domain from blocking element α/δ (BEAD) and the cHS4 CTCF-binding domain. The 12xCTCF insulator contains consecutive repeats of a CTCF-binding domain consensus sequence separated by unique spacers. The 7xCTF/NF1 insulator contains consecutive repeats of the CTF/NF1-binding domain. (b) Insulated FV vector construction. Insulators were inserted into the U3 deletion site of the 3′ LTR. The FV vector DNA is transfected into HEK293 cells to make vector virions. During vector preparation the vector DNA is initially transcribed into RNA, which is encapsidated and reverse transcribed into DNA that is integrated into the host genome. During the process of reverse transcription, the 3′ LTR, including the insulator, is copied to the 5′ LTR so that the integrated provirus is flanked by the insulators. CAR is the cis-acting region containing the remaining portions of the FV gag, pol, and env sequences necessary for vector genome packaging and integration. (c) Insulators block the internal promoter from acting on adjacent host genes.