Maturation of 23S ribosomal RNA requires the exoribonuclease RNase T

Citation
Zw. Li et al., Maturation of 23S ribosomal RNA requires the exoribonuclease RNase T, RNA, 5(1), 1999, pp. 139-146
Citations number
32
Categorie Soggetti
Biochemistry & Biophysics
Journal title
RNA-A PUBLICATION OF THE RNA SOCIETY
ISSN journal
13558382 → ACNP
Volume
5
Issue
1
Year of publication
1999
Pages
139 - 146
Database
ISI
SICI code
1355-8382(199901)5:1<139:MO2RRR>2.0.ZU;2-L
Abstract
Ribosomal RNAs are generally synthesized as long, primary transcripts that must be extensively processed to generate the mature, functional species. i n Escherichia coil, it is known that the initial 30S precursor is cleaved d uring its synthesis by the endonuclease RNase III to generate precursors to the 16S, 23S, and 5S rRNAs. However, despite extensive study, the processe s by which these intermediate products are converted to their mature forms are poorly understood. In this article, we describe the maturation of 23S r RNA. Based on Northern analysis of RNA isolated from a variety of mutant st rains lacking one or multiple ribonucleases, we show that maturation of the 3' terminus requires the action of RNase T, an enzyme previously implicate d in the end turnover of tRNA and in the maturation of small, stable RNAs. Although other exoribonucleases can participate in shortening the 3' end of the initial RNase III cleavage product, RNase T is required for removal of the last few residues. In the absence of RNase T, 23S rRNA products with e xtra 3' residues accumulate and are incorporated into ribosomes, with only small effects on cell growth. Purified RNase T accurately and efficiently c onverts these immature ribosomes to their mature forms in vitro, whereas fr ee RNA is processed relatively poorly, in vivo, the processing defect at th e 3' end has no effect on 5' maturation, indicating that the latter process proceeds independently. We also find that a portion of the 23S rRNA that a ccumulates in many RNase T- cells becomes polyadenylated because of the act ion of poly(A) polymerase I. The requirement for RNase T in 23S rRNA matura tion is discussed in relation to a model in which only this enzyme, among t he eight exoribonucleases present in E. coil, is able to efficiently remove nucleotides close to the double-stranded stem generated by the pairing of the 5' and 3' termini of most stable RNAs.