The structural gene for the ribosomal protein S18 in Escherichia coli. I. Genetic studies on a mutant having an alteration in the protein S18

A mutant of Escherichia coli strain CR341, originally isolated as a temperature-sensitive mutant, was found to have an altered 30 S ribosomal protein (S18) in addition to and independently of temperature sensitivity. Protein S18 from the mutant strain differs in electrophoretic mobility in polyacrylamide gel electrophoresis at pH 4.5 from protein S18 of the parental origin. The mutation responsible for the alteration in S18 is different from two other mutations in the mutant strain which give the temperature-sensitive phenotype. The gene involved in the S18 alteration is located in a region between 76 and 88 minutes on the E. coli genetic map; the location is outside the str-spc region at 64 minutes, where several known ribosomal protein genes are located. An episome covering the loci rha (76 min) through pyr B (84 min) was introduced into the mutant. The resultant merodiploid strains were shown to produce both the normal and the mutant forms of S18. The results support the conclusion described in the accompanying paper (Kahan et al., 1973) that the mutation studied is in the structural gene for S18.