[Synthesis in E. coli cells of short RNA encoded in plasmids]

The synthesis of 5S rRNA and 4.5S RNA in E. coli HB 101 cells harbouring plasmids pKK 5-1 and pKK 247-2 was studied. The plasmids were derived from pBK 322 and contained genes coding for 5S rRNA and 4.5S RNA with regulatory elements of an rRNA transcription operon rrn B. When the cells were grown on enriched or minimal media (2 and 0.3 duplications per hour), the synthesis of both 5S rRNA and 4.5S RNA was proportional to the gene dosage and was greater in the plasmid than in the host strain. Such RNA accumulation did not change the cell growth parameters and was thus not toxic for the cells. At high growth rates, the RNA synthesis in the cells became excessive, and the processing system was upset with the accumulation of RNA precursors. The fact confirms the hypothesis, according to which the whole rRNA operon is essential for its own feedback regulation.