Fig. 5

Functional analysis of SPRE-like elements using a reporter assay. a Schematic representation of the HIV-1 Gag-HiBiT (HG-HiBiT) reporter plasmid. Introduced mutations are indicated by underlining. b Luminous intensities were detected in 293T cells transfected with HG-HiBiT reporter plasmids. Each value was normalized by the luminous intensity from the HG-HiBiT expression plasmid without any additional sequences in 3′ UTR. c, d Functional investigation of C-to-G mutants of SPRE-syn1 and SPRE-syn2. e Functional investigation of SPRE-like elements of mac-syncytin-3; mSyn3, syncytin-Ten1; Ten1, and syncytin-Car1; Car1 by the HG-HiBiT reporter assay in 293T cells. f Functional investigation of SPRE-syn1 and SPRE-syn2 in COS7 (African green monkey), NIH3T3 (mouse), MDCK (dog), and QT6 (quail) by the HG-HiBiT reporter assay. Each value was normalized by the luminous intensity from the HG-HiBiT expression plasmid without any additional sequences in 3′ UTR in each cell line. g Functional investigation of SPRE activities in MLV-Gag and SFV-Gag. Each value was normalized by the luminous intensity of the respective reporter without any additional sequences in 3′ UTR. h Functional investigation of SPRE activities in NanoLuc