Abstract
The Saccharomyces cerevisiae ribosomal stalk is made of five components, the 32-kDa P0 and four 12-kDa acidic proteins, P1alpha, P1beta, P2alpha, and P2beta. The P0 carboxyl-terminal domain is involved in the interaction with the acidic proteins and resembles their structure. Protein chimeras were constructed in which the last 112 amino acids of P0 were replaced by the sequence of each acidic protein, yielding four fusion proteins, P0-1alpha, P0-1beta, P0-2alpha, and P0-2beta. The chimeras were expressed in P0 conditional null mutant strains in which wild-type P0 is not present. In S. cerevisiae D4567, which is totally deprived of acidic proteins, the four fusion proteins can replace the wild-type P0 with little effect on cell growth. In other genetic backgrounds, the chimeras either reduce or increase cell growth because of their effect on the ribosomal stalk composition. An analysis of the stalk proteins showed that each P0 chimera is able to strongly interact with only one acidic protein. The following associations were found: P0-1alpha.P2beta, P0-1beta.P2alpha, P0-2alpha.P1beta, and P0-2beta.P1alpha. These results indicate that the four acidic proteins do not form dimers in the yeast ribosomal stalk but interact with each other forming two specific associations, P1alpha.P2beta and P1beta.P2alpha, which have different structural and functional roles.
Highlights
The ribosomal stalk is an important structural element of the large ribosomal subunit directly associated with the interaction of the elongation factors during the protein synthesis elongation step in bacteria
The amino acid sequence similarity of the prokaryotic and eukaryotic stalk components is rather low [24]. Their structural differences are especially remarkable in the case of P0, which is larger than L10 and contains a carboxyl-end extension of around 100 amino acids not present in the bacterial polypeptide [24]
The overall amino acid sequence identity of the acidic proteins and the replaced P0 segment ranges from 31.5 to 35.4%, which is reduced to around 25% if the identical last 13 residues are excluded
Summary
The ribosomal stalk is an important structural element of the large ribosomal subunit directly associated with the interaction of the elongation factors during the protein synthesis elongation step in bacteria (for a review, see Ref. 1). The amino acid sequence similarity of the prokaryotic and eukaryotic stalk components is rather low [24] Their structural differences are especially remarkable in the case of P0, which is larger than L10 and contains a carboxyl-end extension of around 100 amino acids not present in the bacterial polypeptide [24]. This extension resembles the structure of the acidic P1/P2 proteins, containing a flexible hinge and the same highly conserved 13-amino acid terminal peptide (see Fig. 1). As a consequence of this functional similarity, the proteins P1/P2, in contrast to bacterial L7/L12, are not essential for ribosome activity and cell viability [27]
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