Assignment of the eukaryotic translation initiation factor (EIF2S3) to tammar wallaby chromosome 5p by in situ hybridization.

The gene encoding the eukaryotic initiation factor EIF2S3 (also known as Eif-2Á) is located on the X chromosome, at Xp22.11 in humans, and its homologue Eif2s3 on band C1 in the mouse. EIF2S3 is widely expressed and escapes X inactivation (Ehrmann et al., 1998). In the mouse, expression of a Y homologue (Eif2s3y) has been shown to be essential for spermatogenesis (Mazeyrat et al., 2001). No Y homologue of EIF2S3 has been found in humans. We show here that in the tammar wallaby, a model metatherian mammal, EIF2S3 lies on chromosome 5p along with many other genes from the distal two-thirds of human Xp. Thus EIF2S3 was part of a large autosomal addition to the eutherian X chromosome after the divergence of the metatherians approximately 180 Mya. In mouse, X and Y homologues have diverged, and the Y homologue now has a critical malespecific role. In humans, the Y homologue was lost, perhaps because a testis-specific copy of EIF2S3 has been retroposed to human chromosome 12 (Ehrmann et al., 1998). Materials and methods