Abstract
Processing of ribosomal RNA (rRNA) precursors is an important component of RNA metabolism in all cells. However, in no system have we yet identified all the RNases involved in this process. Here, we show that four 3'→5'-exoribonucleases, RNases II, R, and PH, and polynucleotide phosphorylase (PNPase), participate in maturation of the 3' end of 16S rRNA. In their absence, 16S precursor molecules with 33 extra 3'-nt accumulate; however, the presence of any one of the four RNases is sufficient to allow processing to occur, although with different efficiencies. Additionally, we find that in the absence of 3' maturation, 5' processing proceeds much less efficiently. Moreover, mutant 30S particles, containing immature 16S rRNA, form 70S ribosomes very poorly. These findings, together with the earlier discovery that RNases E and G are the 5'-processing enzymes, completes the catalogue of RNases involved in maturation of Escherichia coli 16S rRNA.
Highlights
The RNases involved in 3Ј maturation of E. coli 16S ribosomal RNA (rRNA) were not known
Exoribonucleases Participate in 3Ј Processing of 16S rRNA— To assess whether exoribonucleases might play a role in 16S rRNA processing, we made use of mutant strains lacking one or more known exoribonucleases
From the ratio of precursor to mature signal, we could determine whether any mutant strain accumulated more precursor than wild type cells. Based on this preliminary screening, we observed that cells deficient in certain combinations of exoribonucleases showed an elevated level of precursor. These data focused our attention on the processive exoribonucleases, RNase II, RNase R, and polynucleotide phosphorylase (PNPase), as well as on RNase PH
Summary
The RNases involved in 3Ј maturation of E. coli 16S rRNA were not known. We show that four 335-exoribonucleases, RNases II, R, and PH, and polynucleotide phosphorylase (PNPase), participate in maturation of the 3 end of 16S rRNA. In their absence, 16S precursor molecules with 33 extra 3-nt accumulate; the presence of any one of the four RNases is sufficient to allow processing to occur, with different efficiencies. Mutant 30S particles, containing immature 16S rRNA, form 70S ribosomes very poorly These findings, together with the earlier discovery that RNases E and G are the 5-processing enzymes, completes the catalogue of RNases involved in maturation of Escherichia coli 16S rRNA
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