Amino-terminal sequence identity of ubiquitin and the nonhistone component of nuclear protein A24

The amino-terminal 37 residues of bovine and human ubiquitin and of the nonhistone component from bovine nuclear protein A24 are identical. The probability that the two proteins are unrelated is infinitesimal. That they share such a highly conserved sequence indicates that they perform a cell function of basic importance and have a common evolutionary origin. They may even be products of the same gene. We make several suggestions concerning their structural and functional relationships based on a correlation of existing information.