Localisation of an endonuclease specific for double-stranded RNA within the nucleolus and its implication in...

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Nucleoli are key sites for ribosomal RNA (rRNA) synthesis and processing.
• Ribosome biogenesis involves intricate RNA processing steps, including cleavage of precursor rRNA molecules.
• Specific enzymes, such as RNases, play critical roles in these maturation pathways.

Purpose of the Study:

• To investigate the enzymatic activity within nucleoli responsible for ribosomal RNA processing.
• To identify the specific RNase involved in cleaving pre-ribosomal RNA transcripts.
• To elucidate the role of double-stranded RNA-specific nucleases in ribosome biogenesis.

Main Methods:

• Enzymatic extraction of nucleolar components using low salt/EDTA.
• Association analysis of enzymatic activity with pre-ribosomal particles (80-S and 55-S).
• In vitro transcription assays under varying ionic conditions to assess RNA processing.
• Addition of purified RNase DII and RNase III to transcription systems.

Main Results:

• A nucleolar enzymatic activity, similar to RNase DII, was identified in chick and mouse cells.
• This enzyme is associated with pre-ribosomal particles.
• Optimal salt conditions for the nucleolar enzyme led to the cleavage of nucleolar transcripts into intermediate-sized molecules.
• Addition of RNase DII or RNase III mimicked the processing observed under optimal conditions.

Conclusions:

• A nucleolar RNase that recognizes double-stranded regions in pre-ribosomal RNA is involved in ribosomal RNA maturation.
• This enzyme facilitates the cleavage of precursor rRNA, contributing to the formation of mature ribosomal RNA.
• The findings highlight the importance of specific RNases in the complex process of ribosome biogenesis.