Analysis of ribosomal proteins in streptomycin resistant and dependent mutants isolated from streptomycin independent Escherichia coli strains.

Mutants resistant to (Str-R) or dependent on streptomycin (Str-D) were isolated from several streptomycin independent (Str-I) strains of Escherichia coli. From 90 of these mutants ribosomes were isolated and the ribosomal proteins analyzed by two-dimensional polyacrylamide gel electrophoresis. The results which are summarized in Tables 1-4 led to the following conclusions: a) The phenotype (Str-R) or Str-D) of the mutants isolated from the Str-I strains strongly depends on the parental strain. b) No other ribosomal proteins than S4, S5 and S12 seem to be altered by mutations leading to dependence on, independence from or resistance to streptomycin. c) The S4 proteins of the analyzed mutants belong to three groups. The ratio between the groups depends more on the origin of the mutants than on their phenotype. d)Eight new types of altered S4 proteins were detected. It is very likely that many, if not all, of the altered S4 proteins originated by frame shift mutations. e) Some of the mutants differ from the wild type by alterations in three ribosomal proteins (S4, S5 and S12). The alteration in one protein, S4, apparently compensates for that in another protein, S5, in such a way that the original phenotype is expressed. These mutants are therefore an excellent tool for studies at the molecular level on the interaction of ribosomal components within the particle.