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Characterization of globin messenger ribonucleic acids in membrane polysomes of mouse reticulocytes
Abstract:
Between 20 and 30% of the polysomes in mouse reticulocytes are associated with the cell membrane fraction. These polysomes are not liberated by washing with 0.5 m KCl and are therefore thought to be attached to membranes. They have the same percentage of polyadenylic acid-containing RNA, as determined by oligo(dT)-cellulose affinity chromatography, as cytoplasmic polysomes. Analysis of the RNA by polyacrylamide gel electrophoresis in aqueous solutions shows that at least 95% of the RNA migrates identically with the cytoplasmic polysomal globin mRNAs. Electrophoresis in 99% formamide resolves the membrane mRNAs into two bands which migrate identically with the cytoplasmic alpha- and beta-globin mRNAs. The molar ratio of the alpha- and beta-globin mRNAs, as determined by quantitating the bands on the formamide gels, is similar to that of the cytoplasmic mRNAs. There is also no difference in biological activity between the two messenger preparations. The polyadenylic acid in the membrane mRNAs, isolated after labeling mice in vivo for 20 hours with (32P)orthophosphate, migrates with the three broad size classes previously shown to be present in the cytoplasmic globin mRNAs. The 32P specific activity of the membrane mRNAs and ribosomal RNA fractions after different times of labeling with 32Pi are similar to those from cytoplasmic polysomes. These observations show that the reticulocyte membranes contain approximately 20% of the cellular globin nRNAs, and that these mRNAs are similar to those from cytoplasmic polysomes.
Insights
Mouse reticulocyte membranes bind a significant portion of globin messenger RNAs (mRNAs). These membrane-associated mRNAs are functionally and structurally identical to cytoplasmic globin mRNAs.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Reticulocyte polysomes are involved in protein synthesis.
- The association of polysomes with cellular structures is not fully understood.
Purpose of the Study:
- To investigate the nature and function of polysomes associated with mouse reticulocyte membranes.
- To determine if membrane-associated globin messenger RNAs (mRNAs) differ from cytoplasmic mRNAs.
Main Methods:
- Oligo(dT)-cellulose affinity chromatography to assess polyadenylic acid content.
- Polyacrylamide gel electrophoresis in aqueous and formamide solutions to analyze RNA.
- In vivo labeling with (32P)orthophosphate to determine RNA specific activity.
Main Results:
- 20-30% of reticulocyte polysomes are membrane-associated and resistant to high salt washes.
- Membrane-associated globin mRNAs are identical in size, polyadenylation, and molar ratio (alpha- and beta-globin) to cytoplasmic mRNAs.
- Both membrane-bound and cytoplasmic globin mRNAs exhibit similar biological activity and 32P specific activity.
Conclusions:
- Reticulocyte membranes contain approximately 20% of cellular globin mRNAs.
- These membrane-associated globin mRNAs are indistinguishable from their cytoplasmic counterparts in terms of structure, polyadenylation, and biological activity.