Metabolic Control of Klebsiella pneumoniae mRNA Degradation by the Availability of Fixed Nitrogen

The chemical and functional stability of Klebsiella pneumoniae mRNAs was dependent on the nitrogen status of the organism. During exponential growth on N2 or NH+4 as N-source the half-lives of mRNAs were 10 and 4 min, respectively. When NH+4-grown cells were starved of NH+4 for 3 h, under which conditions the nitrogen fixation (nif) genes were derepressed, the half-life of mRNAs increased to 20 min. Addition of NH+4 to such N-starved suspensions rapidly destabilized mRNAs with a resultant half-life of 9 min. This destabilization occurred even in the presence of transcription inhibitors, which indicated metabolic control of mRNA degradation. Under most conditions studied the functional decay of nif-specific mRNAs paralleled the decay of bulk mRNAs.