A polysome-membrane binding system from rat liver. I. Basic characterization of the binding system

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Polysomes, the complexes of messenger RNA and ribosomes, are involved in protein synthesis.
• The interaction between polysomes and the endoplasmic reticulum membrane is crucial for the synthesis of specific proteins.

Purpose of the Study:

• To investigate the binding of polysomes to endoplasmic reticulum membranes.
• To understand the fate of ribosomes and nascent protein chains during in vitro protein synthesis.

Main Methods:

• Developed a reaction system using Sephadex G-25 treated post-mitochondrial fraction (Sephadex-PM) from rat liver as a membrane source.
• Utilized radioactive free polysomes from rat liver for in vitro experiments.

Main Results:

• Nascent protein chains on free polysomes were transferred to membranes in vitro, a process requiring protein synthesis.
• Polysome binding to membranes occurred in two steps: initial binding followed by ribosome release during synthesis, leaving nascent chains.
• Some membrane-bound ribosomes released their nascent chains onto the membranes in vitro.

Conclusions:

• Demonstrated a mechanism for nascent chain transfer from free polysomes to ER membranes in vitro.
• Provided insights into the dynamic interaction of polysomes with membranes during protein synthesis.