Partial tRNA deacylation specifically triggers Escherichia coli cell volume reduction.

Limitation of Escherichia coli cell growth rate either by means of continuous 366 nm illumination, which is known to decrease the in vivo acylation level of some tRNA species, or by means of specific inhibitors of tRNA acylation allows the division rate to remain unchanged for a few generations, resulting in cell volume reduction. In contrast the cell volume remains stable or increases after treatment with inhibitors of DNA replication and transcription, or with drugs acting at any other step of protein synthesis. The conclusion that limiting acylation of some tRNA species is the triggering event is confirmed by the use of thermosensitive mutants of aminoacyl-tRNA synthetases or of tRNA (the divE strain mutated in the tRNA1Ser gene). Other cellular responses modulate the expression of cell volume reduction. The relA+ stringent response helps expression of the effect but does not appear to be strictly required. However, cell volume reduction may be masked under conditions triggering the SOS response. The data suggest that tRNA acylation is one of the major steps where cells sense change in their nutrient environment.