Ovalbumin: a secreted protein without a transient hydrophobic leader sequence.

Ovalbumin mRNA was translated in a reticulocyte lysate. The primary translation product starts with methionine derived from Met-tRNAf. When the nascent polypeptide is about 20 residues long, this methionine is removed. The new NH2-terminal glycine is acetylated from acetyl-CoA when the polypeptide is 44 residues long. The sequence of 35 residues at the NH2 terminus of ovalbumin was determined by automated Edman degradation after a method was devised to prevent acetylation during protein synthesis in the reticulocyte lysate. This sequence is the same as that of secreted ovalbumin and does not resemble the transient "signal peptides" associated with most secretory proteins, including three other egg white proteins synthesized in the same cells as ovalbumin.