Evolution of Protamine: a Further Example of Partial Gene Duplication

Abstract

PARTIAL gene duplication has been suggested as an important mechanism in the evolution of proteins¹ on the basis of a study of the repeating structure of the light (α −) chain of the human haptoglobin molecule controlled by the Hp² gene. Support for this hypothesis has come from the discovery in several unrelated proteins of homologous sequences of amino-acids. In ferredoxin from Clostridium pasteurianun, portions of the N-terminal and C-terminal halves are homologous² and these halves of the molecule may have arisen by partial gene duplication from an intermediate nonadecapeptide which in turn could have been derived by the same processes of duplication from an archetypal tetrapeptide^2,3. Other examples of internal homology have been postulated in cytochrome C (ref. 3), the haemoglobin chains⁴ and the light and heavy chains of immunoglobins⁵.