STABLE RNA, including rRNA and tRNA, turns over slowly, if at all, during steady state growth of Escherichia coli1–4. It is evident, however, that E. coli cells can degrade stable RNA, which is slowly broken down to various extents under such conditions as starvation phosphate5,6, magnesium7,8, potassium9 and nitrogen10,11 The mutant described here very rapidly degrades what is essentially all its stable RNA when RNA synthesis is stopped in cultures at 42° C. The degradation can be prevented if antibiotics are added that inhibit breakdown of polysomes.