The DNA complementary to RNA (cDNA) of the ribosomal stalk protein BmP0 of the silkworm Bombyx mori was isolated from a cDNA library and was subsequently expressed in the conditional P0-null mutant Saccharomyces cerevisiae D67dGP0, whose ribosomes also lack the other stalk components, proteins P1/P2. The transformed strain was able to grow under restrictive conditions, indicating that in the absence of the P1/P2 proteins BmP0 can bind to the yeast ribosomes and complement the lack of the endogenous YP0 protein. In addition, the binding capacity of the B. mori ribosomal stalk components to the ribosomal particle was studied by means of high salt treatment of purified ribosomes. The BmP0 protein retained its binding to the ribosome, suggesting a stable association with the rRNA, in contrast to the acidic proteins BmP1 and BmP2, which were easily released. The results clearly indicate that, as opposed to recent in vitro results, BmP0 does not require the presence of P1/P2 proteins in order to bind to the ribosome.