Comparison of the NH2-terminal sequence of ovalbumin as synthesized in vitro and in vivo.

The sequence of the NH2-terminal 35 residues of chicken ovalbumin was found to be identical with that of the product translated in vitro from the corresponding mRNA. Together with our previous results (Palmiter, R.D., Gagnon, J., and Walsh, K.A. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 94-98), these data show that the only co-translational processing event at the NH2 terminus of the primary translation product is the replacement of the initiator methionine by an acetyl group. Thus, secretion of this major protein by chick oviduct does not involve the cleavage of a "signal peptide" as is characteristic of three other egg white proteins secreted by the same cells.