5S rRNA gene deletions cause an unexpectedly high fitness loss in Escherichia coli

In Escherichia coli, ribosomal RNAs (16S, 23S and 5S) are co-transcribed in a highly regulated manner from seven genomically dispersed operons. Previous studies on the cellular effects of altered levels of two of these rRNAs (16S and 23S) have been useful in better understanding the regulation of rRNA expression. Furthering these studies, we have investigated the effect of 5S rRNA deficiencies on cell fitness through the sequential deletion of 5S rRNA genes. Our findings indicate that the loss of 5S rDNA from multiple genes decreases cell fitness more rapidly than loss of a similar number of 16S and 23S rRNA genes. These results suggest that the cell's innate ability to up-regulate rRNA operons does not compensate for 5S rRNA deficiencies, as was previously shown for 16S and 23S rRNAs. A plasmid-borne 5S rRNA gene is able to compensate for the deleted 5S rRNA genes.