The Tarsius γ-Globin Gene: Pseudogene or Active Gene?

Abstract

We sequenced the ∼5-kb long γ-globin gene locus from Tarsius bancanus and compared it to the published γ-globin gene sequence from the related species Tarsius syrichta. The T. syrichta gene's promoter lacks the distal CCAAT box and has a point mutation in the functionally important proximal CCAAT box (CCgAT). This previous finding had suggested that in tarsiers the γ-globin gene might be a nonexpressed pseudogene. The two tarsier species show the same point mutation at the third nucleotide of the proximal CCAAT element and absence of the distal CCAAT element. Nevertheless, our results indicate that in tarsiers the γ-globin gene is active, since all three coding regions show only synonymous substitutions and a much lower level of divergence than the noncoding regions. This is significantly different from what would be expected for a silent gene evading stabilizing selection. Thus, we hypothesize that the tarsier's γ-globin gene locus is expressed even with the mutation in the proximal CCAAT box.