Ovalbumin utilizes an NH2-terminal signal sequence.

Area of Science:

• Molecular Biology
• Cell Biology
• Protein Biochemistry

Background:

• Protein glycosylation and segregation are crucial post-translational modifications.
• The "signal" sequence directs proteins to specific cellular compartments, like the endoplasmic reticulum.

Purpose of the Study:

• To determine the critical timing for microsome addition during ovalbumin synthesis for glycosylation and segregation.
• To investigate the location of the ovalbumin "signal" sequence.

Main Methods:

• Synchronized translation experiments using wheat germ and reticulocyte lysate systems.
• Addition of dog pancreatic microsomes at different time points during ovalbumin synthesis.

Main Results:

• Ovalbumin glycosylation and segregation occurred only when microsomes were added before the nascent polypeptide chain had 150 amino acids.
• This finding suggests the "signal" sequence is located prior to residue 150.

Conclusions:

• The timing of microsome addition is critical for the proper processing of ovalbumin.
• The "signal" sequence of ovalbumin is likely located before amino acid residue 150, contradicting previous reports.