Expression of ribosomal protein genes in Escherichia coli

Summary

Streptomycin or spectinomycin treatment of an E. coli strain, carrying the str^R and spc^R alleles on the chromosome and the wild-type (sensitive) alleles on the episome, selects for inactivation of the relevant sensitive allele. After Mu induced mutagenesis, in the absence of selection against extended deletions upon the episome, a large proportion of str^o mutants are also spc^o, and vice versa. However, when markers flanking the strA and spcA gene cluster are simultaneously selected, effectively eliminating long deletions, the majority of str^o mutants continue to express the spc^s allele, and vice versa.

Insofar as inactivation after Mu treatment is due to prophage insertion within or proximal to the genes in question, this result indicates that the genes strA and spcA are not parts of a single operon. In virtue of the high frequency of extended deletions observed in the absence of suitable counter-selection, we must place a word of caution upon the use of phage Mu-1 as a means for isolating polar mutations and defining transcriptional units.