Discovery of novel N-terminal segment DNA-binding domains for GTF2IRD2 and GTF2I. (A) Two classes of novel isoforms were identified for the human-specific duplicate gene GTF2IRD2 (transcribed from right to left in this view), shown above the current NCBI gene annotations. The upper isoform consists of an out-of-frame gene fusion to upstream gene STAG3L2 while the lower isoform includes an alternative first exon, derived from a DNA transposon (TcMar-Tigger family), yielding a new N-terminal segment. (B) The proposed GTF2IRD2 isoform contains two additional N-terminal DNA-binding domains (helix-turn-helix domain and a Tc5 transposase DNA-binding domain) derived from the DNA transposon Tigger7. (C) A multiple sequence alignment of the newly identified N-terminus predicted protein sequences shows conservation among primates. (D) A heatmap of expression levels estimated using Kallisto across tissues (GTEx) shows that the canonical form is more broadly expressed than the transposon-containing isoform with the exception of the testis.
