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#rRNA processing

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Processing of rRNA and tRNA

Major role of rRNA processing is

Maturation of ribosomal RNA serves principal purpose of ribosome assembly rather than gene regulation or degradation alone. Processing cleaves polycistronic or 45S precursors, removes internal and external spacers, incorporates chemical modifications and coordinates binding of ribosomal proteins to produce functional 30S, 50S or 40S, 60S subunits. Modifications fine-tune decoding and peptidyl transferase function. Proper assembly guarantees translation competence, nucleolar surveillance, stress responses, and overall cellular growth control, linking rRNA biogenesis rate to cell proliferation demands. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Watson Molecular Biology of the Gene, 7th ed., Chapter 15, rRNA processing and ribosome assembly pathway

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Processing of rRNA and tRNA

Internal transcribed spacer is abbreviated as

Within the 45S pre-rRNA, coding regions for mature rRNAs are separated by Internal Transcribed Spacer sequences: ITS1 between 18S and 5.8S, ITS2 between 5.8S and 28S. Unlike NTS, ITS regions are transcribed by Pol I as part of precursor but subsequently excised during maturation by nucleolar processing machineries including RNase MRP and exonucleases like Xrn2 and exosome. Their removal liberates individual rRNAs. Due to rapid evolution and variability, ITS sequences serve as universal DNA barcodes for fungal and plant phylogenetics.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8, Internal transcribed spacers ITS1 and ITS2 excision

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Processing of rRNA and tRNA

Primary rRNA transcript in E. coli is processed by

In Escherichia coli, seven rrn operons produce about 30S primary precursor containing leader, 16S, spacer tRNAs, 23S, 5S and trailer. Maturation initiates with RNase III, a Mg2+-dependent double-strand specific endoribonuclease that cleaves long inverted repeat stems flanking 16S and 23S, co-transcriptionally. Cleavage liberates pre-16S 17S, pre-23S and 9S 5S precursors carrying extra nucleotides at both ends. Subsequent processing by RNase E, RNase G, RNase PH, RNase T, PNPase removes leaders and trailers, generating mature termini essential for subunit assembly and translation activity.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6, Processing of bacterial 30S pre-rRNA by RNase III

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