Messenger RNA binding protein purified from reticulocyte polyribosomes

Area of Science:

• Molecular Biology
• Protein Biochemistry
• RNA Binding Proteins

Background:

• Polyribosomes are complexes of messenger RNA (mRNA) and ribosomes involved in protein synthesis.
• Certain proteins associated with polyribosomes are crucial for mRNA binding and translation regulation.
• Understanding these proteins is key to deciphering gene expression mechanisms.

Purpose of the Study:

• To purify and characterize a specific protein from rabbit reticulocyte polyribosomes that binds poly(A)-rich mRNA.
• To investigate the subunit composition, molecular weight, and binding specificity of the purified protein.

Main Methods:

• Purification using ammonium sulfate fractionation and multiple column chromatography techniques (phosphocellulose, hydroxylapatite, DEAE-cellulose).
• Determination of molecular weight and subunit composition via Sephadex G-200 chromatography and rate-zonal sedimentation.
• Isoelectric focusing polyacrylamide gel electrophoresis to determine the protein's isoelectric point.
• RNA binding competition assays to assess specificity.

Main Results:

• A protein that binds poly(A)-rich mRNA was purified to apparent homogeneity.
• The protein consists of two subunits (66,700 and 56,400 apparent molecular weights) in a 1:1 stoichiometry, with an estimated native molecular weight of 110,000.
• The protein exhibited specific binding for poly(A)-rich mRNA, with other RNAs being significantly less effective competitors.
• Interestingly, poly(riboguanylic acid) competed even more effectively than mRNA.

Conclusions:

• A novel mRNA-binding protein with specific affinity for poly(A)-rich mRNA has been isolated and characterized.
• The protein's subunit composition and specific binding properties suggest a role in mRNA metabolism or translation.
• The unexpected high affinity for poly(riboguanylic acid) warrants further investigation into the protein's RNA binding mechanisms.