Ribosomal assembly defectivity in a set of amber mutants of Escherichia coli.

Five amber mutations affecting essential genes of $\text{Escherichia coli}$ have been isolated. The procedure relies on P1-mediated localized mutagenesis(1) and on the use of a recipient strain carrying a strong but instable suppressor gene and a particular thermoinducible λ prophage which kills suppressor hosts at 42°C (2). All five mutations map close to the $\text{spcA}$ gene, in a region which codes essentially for ribosomal proteins. Strains harboring the mutations were studied biochemically; all five exhibit defective ribosomal assembly upon loss of suppression.