A lethal mutation which affects the maturation of ribosomes

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Escherichia coli mutants can exhibit temperature sensitivity affecting survival.
• Carbon starvation impacts bacterial recovery and cellular processes.
• Ribosomal RNA (rRNA) synthesis and maturation are crucial for bacterial viability.

Purpose of the Study:

• To investigate the cause of temperature-sensitive lethality in an Escherichia coli mutant.
• To identify the specific cellular process affected by the mutation.
• To characterize the genetic basis of the observed phenotype.

Main Methods:

• Temperature shift experiments to a nonpermissive temperature (43°C).
• Antibiotic sensitivity assays targeting protein and DNA synthesis.
• Analysis of RNA and protein synthesis capacities.
• Ribosomal protein and RNA analysis, including precursor RNA maturation.
• Genetic mapping using three-point transduction crosses.

Main Results:

• The mutant showed irreversible cell death at 43°C, with a half-life of 30 minutes.
• Bactericidal effects were reversed by antibiotics inhibiting protein synthesis, not DNA synthesis.
• At 43°C, RNA and protein synthesis decreased before DNA synthesis.
• rRNA maturation was impaired, with slow conversion of 17S precursor to 16S rRNA.
• A single mutation, designated rimH, affecting rRNA maturation, was identified and mapped.

Conclusions:

• The mutation rimH affects a late step in ribosomal RNA maturation in Escherichia coli.
• This pleiotropic mutation leads to temperature-sensitive lethality and impaired protein synthesis.
• The rimH gene maps outside known ribosomal structural gene clusters, suggesting novel regulatory mechanisms.