The histidine-rich protamine from ostrich and Tinamou sperm. A link between reptile and bird protamines

We have characterized for the first time the proteins of two different spec ies of palaeognathous birds, Struthio camelus australis (ostrich) and Notho procta perdicaria sanborni (Chilean tinamou. Similar to what had been previ ously reported in neognaths, the electrophoretic mobility, amino acid compo sition, and primary structure of the main protamine (P-II) component of the se two species of birds are similar. However, in contrast to neognathous bi rds, the protamines from paleognaths display a higher electrophoretic mobil ity and a significantly different amino acid composition and protein sequen ce. The sperm and the main protamine component P-II from the ostrich reveal structural and compositional characteristics intermediate between neognath ous birds and reptiles. The marked differences between the protamines and s perm structure of neognaths and paleognaths provide support to a phylogenet ic relationship between neornithine birds in which these two groups represe nt two separate phylogenetic lines. Furthermore, these results shed some ad ditional light on the controversial origin of birds. They provide further m olecular support to the fossil record that suggests that reptiles and birds an closely related.