Synthesis of poly(A)+-containing RNA during growth in Escherichia coli relA+ and relA- strains

There are very different results on the synthesis of poly(A)+-containing RNA in bacteria. We, therefore, studied the influence of growth and amino acid starvation on the synthesis of poly(A)+-RNA in a relA+ and relA- strains of E. coli. Only the relA+ strains is able to respond to an amino acid limitation by production of ppGpp which causes a strong reduction of stable RNA transcription. During growth we observed significant alterations of the percentage of [3H]-uridine labelled total RNA which bound to poly(U)-sepharose (% poly(A)-RNA). It was mainly influenced by drastic changes of the synthesis of non-polyadenylated stable RNA (rRNA, tRNA) during growth and, therefore, it did not reflect the actual synthesis of polyadenylated mRNA. An amino acid starvation induced in the relA+ strain a stronger and more rapid reduction of the transcription of non-polyadenylated RNA as well as of poly(A)+-RNA than in the relA- strain which did not produce ppGpp under these conditions. Therefore, we conclude that ppGpp inhibited not only the synthesis of the non-polyadenylated stable RNA but also that of poly(A)+-containing mRNA, although the latter was apparently less affected.