Fig. 1.

SETMAR second isoform is specific to anthropoid primates.

A, The human SETMAR gene encodes two major isoforms, the full-length protein (isoform 1) and a truncated protein (isoform 2). The second isoform is methyltransferase deficient because the majority of the SET and post-SET domains are removed. Canonical donor site (DS), lariat branch points (LBP), and acceptor splicing site (ASS) are present in the second exon of SETMAR. The top brackets represents the exon codons. B, Phylogenetic tree of the second exon of SETMAR in several mammals. Although the 5′ donor site is absent in the marmoset [4], it must have appeared before the emergence of primates because it is present in several non-primates mammals. The 3′ acceptor site is specific to anthropoid primates except for the old-world monkeys which lost it owing to a single point mutation.