RIBOSOME RECYCLING FACTOR (RIBOSOME RELEASING-FACTOR) IS ESSENTIAL FOR BACTERIAL-GROWTH

Ribosome releasing factor, product of the frr gene in Escherichia coli , is responsible for dissociation of ribosomes from mRNA after the ter mination of translation. It functions to ''recycle'' ribosomes and is renamed ribosome recycling factor in this paper. An E. coil strain was constructed (MC1061-2), which carried frame-shifted frr in the chromo some and wild type frr on a temperature-sensitive plasmid. MC1061-2 is temperature-sensitive in its growth and does not segregate its frr-ca rrying plasmid under the plasmid incompatibility pressure. In contrast , isogenic E. coli carrying wildtype frr in the chromosome and mutated frr on the temperature-sensitive plasmid is not temperature-sensitive in its growth and segregates its plasmid from incompatible plasmids. All spontaneously formed thermoresistant colonies derived from MC1061- 2 carried wild-type frr that resided either in the bacterial chromosom e by re-exchange or in the plasmid, which became temperature-resistant . These observations establish that frr is an essential gene for cell growth.