Fig. 4

Identification of SPRE-like elements in different mammalian syncytin genes. a Schematic representation of SPRE-like elements in mac-syncytin-3, syncytin-Ten1, and syncytin-Car1. b, c Fusion-dependent luciferase assay in mac-Syncytin-3 and Syncytin-A using 293T cells. Each syncytin gene was cloned into the phCMV3 plasmid with or without 3′ UTR. A SPRE-core motif mutation similar to Fig. 2a was introduced into mac-syncytin-3. d Schematic representation of minigene plasmids of syncytin-1; pWE1 and syncytin-2; pFRDE1. The CMV enhancer and promoter were introduced upstream of the genes to enhance gene expression. CE; CMV enhancer, CP; CMV promoter. e Fusion-dependent luciferase assay of 293T cells transfected with pWE1 and pFRDE1. f Northern blot analysis in transcripts from 293T cells transfected with pWE1 and pFRDE1 minigenes with or without SPRE mutation. The arrowheads indicate the mRNA. g Poly(A) tail-targeted PCR in pWE1 transcripts