Can the product of the θ gene be a real globin?

Abstract

A new member (θ1, or ψα) of the α-globin gene family has recently been identified in a number of species^1–5. In higher primates the θ1 gene has all the structural features apparently necessary for expression, and it appears to have long been under strong selective constraints which suggests that it could still be, or recently have been, a functional gene². No corresponding 'globin' has yet been identified, however. In somether species, galago⁵ and rabbit⁴ for example, the θ1 and ψα genes have accumulated enough inactivating mutations for them to be considered genuine pseudogenes. Horses also have an α-like gene (ψα) (ref. 3), in a 3' position identical to the other species in relation to the functional α genes, and this also appears to have the elements required for a functional gene. The predicted amino-acid sequence, however, suggests that any 'globin' product is likely to be non-viable because it has a number of seriously deleterious amino-acid replacements. Some of these amino-acid changes are shared with the rabbit and primate sequences, indicating that they predate the mammalian radiation, and that if indeed any of these genes are still functional, they are unlikely to be making haemoglobin.