Stability of "spacer" sequences of pre-ribosomal RNA in Escherichia coli

Processing of Escherichia coli 16S rRNA with bacteriophage lambda leader sequences

To test whether any specific 5' precursor sequences are required for the processing of pre-16S rRNA, constructs were studied in which large parts of the 5' leader sequence were replaced by the coliphage lambda pL promoter and adjacent sequences. Unexpectedly, few full-length transcripts of the rRNA were detected after the pL promoter was induced, implying that either transcription was poor or most of the rRNA chains with lambda leader sequences were unstable. Nevertheless, sufficient transcription occurred to permit the detection of processing by S1 nuclease analysis. RNA transcripts in which 2/3 of the normal rRNA leader was deleted (from the promoter up to the normal RNase III cleavage site) were processed to form the normal 5' terminus. Thus, most of the double-stranded stem that forms from sequences bracketing wild-type 16S pre-rRNA is apparently not required for proper processing; the expression of such modified transcripts, however, must be increased before the efficiency of processing of the 16S rRNA formed can be assessed.

Control of ribosomal RNA synthesis in Escherichia coli. II. Ribosomal RNA synthesis in isolated nucleoids

The effect of amino acid-starvation on the transcription in vitro of overall RNA and ribosomal RNA was investigated using nucleoids prepared from the exponentially growing and the amino acid-starved cells of rel+ and rel- strains of Escherichia coli. In this system, the synthesis of RNA is exclusively due to elongation of the chains which have been initiated in vivo. The amounts of overall and ribosomal RNA synthesized per unit of DNA in the nucleoids were analyzed for each preparation. The following observations have been made. (1) The total RNA synthesis per unit of DNA in the nucleoids from the amino acid-starved rel+ and rel- cells was not significantly different from each other. (2) The preferential ribosomal RNA synthesis occurred in the nucleoids from the growing cells; the ribosomal RNA synthesis was restricted in the nucleoids from the starved rel+ cells, while no restriction was observed in the nucleoids from the starved rel- cells. The results suggest that the ribosomal RNA synthesis is regulated at the initiation or less likely elongation level of the transcription. (3) A ribosomal RNA of a discrete size of about 30S was synthesized in the nucleoids. No mature ribosomal RNA species was produced in this system. The 30S RNA is probably a primary transcript of ribosomal RNA genes containing 23S, 16S and 5S mature ribosomal RNA sequences.