Abstract

The stalk of the large ribosomal subunit is involved in the interaction of the elongation factors with the ribosome, as biochemical data have clearly indicated and as has been directly confirmed by electron microscopy. The eukaryotic ribosomal‐stalk elements are functionally equivalent to the bacterial components, but while some of them are highly conserved, others have evolved notably. The highly probable presence of the acidic proteins in the ribosome as monomers, together with the existence of one specific binding site for each 12‐kDa protein in the particles, favors the homogeneous rather than the heterogeneous ribosomal‐stalk model in yeast. The data available on the assembly of the yeast stalk are not abundant. An analysis of two Saccharomyces cerevisiae strains carrying a disruption of the genes encoding the two proteins of the same type, either P1 or P2, has shown that their ribosomes do not carry any 12‐kDa acidic protein. The experimental evidence indicates that the in vitro assembly of the yeast ribosomal stalk involves a number of consecutive binding steps which are apparently initiated by the interaction of the P1 proteins and is followed by the binding of the P2 polypeptides.