Nascent chicken ovalbumin contains the functional equivalent of a signal sequence.

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Abstract
Highly purified mRNA for chicken ovalbumin was translated in a cell-free protein synthesizing system from rabbit reticulocytes in the presence or absence of EDTA-stripped microsomal membranes from dog pancreas. Nascent, but not completed, ovalbumin was transferred across the microsomal membrane, as demonstrated by cotranslational core glycosylation of ovalbumin nascent chains, by resistance to posttranslational proteolysis of only the glycosylated ovalbumin chains, and by cosedimentation with the membrane of exclusively the glycosylated form. Nascent chains of bovine prolactin competed with nascent ovalbumin for transfer across the microsomal membrane. However, no competition for membrane sites was observed between nascent chains of rabbit globin and either nascent ovalbumin or prolactin. Nascent ovalbumin may contain the functional equivalent of a signal sequence for transfer across membranes, and membrane components involved in the segregation of secretory proteins with cleaved signal sequences may also function in the segregation of ovalbumin.