TheGON4Lb gene and its duplicate YY1AP1. (A) Schematic representation of the genomic organization of GON4Lb and YY1AP1. Start codons and stop codons are marked with black arrows and stop signs, respectively. Insertion of an Alu-exon to the transcript of YY1AP1 insert a premature termination codon (PTC) (B) Multiple alignment of the alternative Alu-exon of YY1AP1 and the relative intronic region of GON4L. Splice sites are marked with black arrows. Substitutions and deletions relative to the original gene are marked in pink. (C) Exonization of an Alu exon in YY1AP1, and not in the original gene, as shown by RT-PCR analysis of U2OS cell line. Primers were designed to the flanking exons of each copy.