Initiation of translation is impaired in E. coli cells deficient in 4.5S RNA

The 4.5S RNA of Escherichia coli is a small, stable RNA that is essential for cell growth but its function is not yet known. Its biosynthesis is stringently controlled, and it is processed by RNase P, a transfer RNA processing enzyme. To identify the biological role of the 4.5S species, we have characterized the physiological changes that occur when the bacterial cell is depleted of this RNA. We used a strain of E. coli in which synthesis of the 4.5S RNA can be turned off by removing an inducer of the Iac operon, resulting in cell death. We report here that an early consequence of depriving the cell of 4.5S RNA is the accumulation of translationally-defective ribosomes, which maintain their ability to elongate polypeptide chains, but can no longer participate in the initiation of protein synthesis.