On the GTP-ase activity induced by an acidic protein present in 50S ribosomes of Escherichia coli
✍ Scribed by W. Möller
- Publisher
- Elsevier Science
- Year
- 1972
- Weight
- 290 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0022-0728
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✦ Synopsis
Bacterial ribosomes consist of two subunits, the larger 50S and the smaller 30S. Both subunits have a protein to RNA ratio of about 1:2. The larger subunit contains 23S RNA of mol.wt. 1.1 x 106 and the smaller subunit contains 16S RNA of mol.wt. 0.55 X 10 6. The proteins of ribosomes are very complex. In the 30S ribosome there are about 20 different proteins all with one exception in the mol.wt, range of 10,000-25,000; in the 50S ribosome there are about 35 different proteins in a similar range ofmol.wt. In recent years conclusive evidence has been presented to show that the amino acid sequences of the proteins of ribosomes differ from each other 1"2.
Although our knowledge of the fine structure of ribosomal proteins grows, the contribution of each protein to the initiation, elongation or termination step of protein biosynthesis has not been determined. Certainly the ribosomal RNA serves somehow as a matrix for part of the basic proteins but if one seeks hard facts to vindicate the classification of structural vs. enzymic proteins, any subdivision seems arbitrary.
Considerable progress has "been made in delineating the primary structure of the RNA a. Moreover it has been found that several proteins display unique binding properties to distinct sections of the RNA 4. Such a localized and specific "snapping in" of individual proteins has been suggested before 5.
In addition to basic proteins, the ribosome contains also a few acidic proteins 6. These are released from the particles at a high concentration of CsCI and on removal of salt they reassociate with the "cores" with recovery of the original particle activity.
In this paper we discuss shortly the structure and function of a 50S acidic ribosomal protein, referred to as A-protein. This protein is involved in translocation and thereby supplies an example of a functional ribosomal protein. Interestingly, the structural properties of A-protein resemble those of contractile proteins. A more general analogy between ribosomal and contractile protein systems has been noted by Nishizuka and Lipmann 7 and subsequently by Hill 8. *Dedicated to Professor J. Th. G. Overbeek on the occasion of the 25th anniversary of his appointment as a Professor of Physical Chemistry.