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After B. Wittmann-Liebold, in "Structure, Function, and Genetics of Ribosomes" (B. Hardesty and G. Kramer, eds.), p.331, Springer-Verlag, New York, 1986.

After B. Wittmann-Liebold, in "Structure, Function, and Genetics of Ribosomes" (B. Hardesty and G. Kramer, eds.), p.331, Springer-Verlag, New York, 1986.

Separation in the above system provides the basis of the nomenclature of ribosomal proteins (Kaltschmidt & Wittmann, 1970). It has been proposed that ribosomal proteins be designated by numbering in a downward direction, as seen from the two-dimensional electrophoretic separation patterns (Figs. 7.1 and 7.2). Proteins of the small ribosomal subunit (30S or 40S) are denoted by the letter S (S1, S2, S3, etc.), while proteins of the large subunit (50S or 60S) are designated by the letter L (L1, L2, L3, etc.). The small E. coli ribosomal subunit contains 21 proteins, from S1 to S21. The large ribosomal subunit contains 32 different proteins, from L1 to L34; the spot initially referred to as L8 is not an individual protein but a complex between proteins L10 and L12; the spots designated as L7 and L12 correspond to the same protein, L7 being the N-acetylated derivative of L12. Protein S20 of the small ribosomal subunit is identical to protein L26 of the large subunit. Therefore, there are 52 different ribosomal proteins in the E. coli 70S ri-bosome.

The acidic L7/L12 protein present in E. coli ribosomes (120 amino acid residues, molecular mass 12,200 daltons) is unique in the sense that there are four molecules of this protein per ribosome; it appears to form a tetramer with a molecular mass of about 50,000 daltons. With this exception, all other proteins in the E. coli ribosome seem to be present in a single copy per ribosome. The sizes of E. coli ribosomal proteins are given in Table 7.1..

Originally ribosomal proteins of each species had their own nomenclatures, according to their own electrophoretic patterns. Thus, the E. coli ribosomal proteins were designated as EcS1, EcS2, ... EcL1, EcL2, etc., the ribosomal proteins of Bacillus stearithermophilus - as BsS1, BsS2, etc., those of Thermus thermophilus - TtS1, TtS2, etc.. Similarly, the ribosomal proteins of yeast (Saccharomyces cerevisiae) have the prefix Y, rat - R, human - H. Naturally, the same protein number may refer to non-analogous proteins of different species. Now, when it becomes clear that most ribosomal proteins are evolutionary conserved, the homology between proteins of different species can be found and thus the relation of proteins can be established. This creates the ground for a universal nomenclature. The universal nomenclature for ribosomal proteins of bacteria, including eubacteria and archaea, based on the protein numbers of E. coli ribosomes is already in operation. The universal nomenclature for eukaryotic ribosomal proteins based on the protein numbers of rat or human ribosomes has been also recently introduced. The correlation between

Table 7.2. Correlation (homology) between prokaryotic (eubacteria and archaea) and eukaryotic (fungi and mammals) ribosomal proteins.

Escherichia coli Halobacterium marismortui

Yeast Rat

Escherichia coli Halobacterium marismortui

Yeast Rat

Ec or Hm S2

Y or RSa

Ec or Hm L2

Y or RL8

0 0

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