The ribosomal P-proteins of the medfly Ceratitis capitata form a heterogeneous stalk structure interacting with the endogenous P-proteins, in conditional P0-null strains of the yeast Saccharomyces cerevisiae

The genes encoding the ribosomal P-proteins CcP0, CcP1 and CcP2 of Ceratiti s capitata were expressed in the conditional P0-null strains W303dGP0 and D 67dGP0 of Saccharomyces cerevisiae, the ribosomes of which contain either s tandard amounts or are totally deprived of the P1/P2 proteins, respectively . The presence of the CcP0 protein restored cell viability but reduced the growth rate. In the W303CcP0 strain, all four acidic yeast proteins were fo und on the ribosomes, but in notably less quantity, while a preferable bind ing of the YP1 alpha/YP2 beta pair was established. In the absence of the e ndogenous P1/P2 proteins in the D67CcP0 strain, the complementation capacit y of the CcP0 protein was considerably reduced. The simultaneous expression of the three medfly genes resulted in alterations of the stalk composition : both the CcP1 and CcP2 proteins were found on the particles substituting the YP1 alpha and YP2 alpha proteins, respectively, but their presence did not alter the growth rate, except in the case of the YP1 alpha/beta defecti ve strain, where a helping effect on the binding of the YP2 alpha and YP2 b eta proteins on the ribosomes was confirmed. Therefore, the medfly ribosoma l P-proteins complement the yeast P-protein deficient strains forming an he terogeneous ribosomal stalk, which, however, is not functionally equivalent to the endogenous one.