This study documents the presence of three acidic proteins, A1 (pI 4.95), A2 (pI 4.85), and A3 (pI 4.70), in Dictyostelium discoideum ribosomes. All three proteins showed an apparent molecular mass of 13 000 by two-dimensional, sodium dodecyl sulfate gel electrophoresis. They were selectively released by treatment of ribosomes with 50% ethanol – 1 M NH4Cl. The amino acid compositions of A1, A2, and A3 were identical and indicated a predominant amount of alanine. All the above properties are shared by Escherichia coli proteins L7 and L12 and acidic ribosomal proteins in many eukaryotes. Unlike other eukaryotic systems, the acidic proteins of D. discoideum were found associated with the 40S rather than the 60S ribosomal subunit. Acidic proteins analogous in size and electrophoretic mobility to those of D. discoideum were also detected in several other cellular slime mold strains. Not one of the cellular slime mold acidic proteins reacted with antibodies to E. coli proteins L7 and L12 in immunodiffusion tests. In D. discoideum, the distribution of acidic proteins was altered during development. Amoebae contained all three proteins. In spores, A, was absent and the relative amounts of A2 and A3 were lower than in amoebae. In addition, nine other acidic ribosomal proteins exhibited differences between vegetative amoebae and spores.Key words: acidic ribosomal proteins, development, cellular slime mold, L7 and L12 proteins, two-dimensional gel electrophoresis.
Independent genes coding for three acidic proteins of the large ribosomal subunit from Saccharomyces cerevisiae.
