Ribosomal protein interactions in yeast. Protein L15 forms a complex with the acidic proteins

Protein L15 from Saccharomyces cerevisiae ribosomes has been shown to interact in solution with acidic ribosomal proteins L44, L44' and L45 by different methods. Thus, the presence of the acidic proteins changes the elution characteristics of protein L15 from CM-cellulose and DEAE-cellulose columns and from reverse-phase HPLC columns. Moreover, immunoprecipitation using anti-L15 specific monoclonal antibodies coprecipitates the acidic proteins, too. Conversely, antibodies raised against the acidic proteins immunoprecipitate protein L15. This coprecipitation seems to be specific since it does not involve other ribosomal proteins present in the sample. Similarly, plastic-adsorbed antibodies specific for one of the components in the L15--acidic-protein complex are able to retain the other component of the complex but cannot bind unrelated proteins. Moreover, protein L15 can be chemically cross-linked to the acidic proteins in solution. These results indicate that protein L15 might be equivalent to bacterial ribosomal protein L10 in forming a complex with the acidic proteins. Since, on the other hand, protein L15 has been shown to be immunologically related to bacterial protein L11 [Juan Vidales et al. (1983) Eur. J. Biochem. 136, 276-281] and to interact with the same region of the large ribosomal RNA as does protein L11 [El-Baradi et al. (1987) J. Mol. Biol. 195, 909-917], these results suggest strongly that protein L15 plays the same role in the yeast ribosome as proteins L10 and L11 do in the bacterial particles.