Molecular conservation of 74 amino acid sequence of ubiquitin between cattle and man

Abstract

UBIQUITIN (originally ‘ubiquitous immunopoietic polypeptide’ or ‘UBIP’)¹ induces lymphocyte differentiation and was first found in bovine thymus during isolation of the thymic polypeptide hormone thymopoietin (originally ‘thymin’)² which induces T-cell differentiation³ and has secondary effects on neuromuscular transmission². Ubiquitin, which has a molecular weight of 8,451, is interesting for several reasons. First, it induces differentiation of T cells and, unlike thymopoietin, B cells¹. Second, both properties are inhibited by the β-adrenergic blocking agent propranolol, and so the capacity of ubiquitin to induce lymphocyte differentiation seems to depend on reaction with a β-adrenergic receptor. Third, ubiquitin activates adenyl cyclase in lymphocyte precursors and in other tissues, again through a, β-adrenergic receptor (M. Bitensky, and G. G., unpublished). Finally, ubiquitin, as the name implies, is found not only in thymus but in all other animal cells and in yeasts, bacteria and higher plants¹. Although its physiological function remains unknown, ubiquitin must be vital to the living cell to have been conserved over such a long evolutionary time span. We have reported the complete primary structure of bovine ubiquitin⁴—a single polypeptide chain of 74 amino acids—and now report that human ubiquitin has an identical sequence.