The ribosomal-RNA-processing pathway in Schizosaccharomyces pombe

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Ribosome biogenesis involves processing precursor RNA into mature ribosomal RNAs (rRNAs).
• Eukaryotic rRNA maturation is complex and rapid, hindering detailed pathway elucidation.
• Phylogenetic comparisons aid in identifying critical events in biological pathways.

Purpose of the Study:

• To determine the major ribosomal RNA (rRNA) processing pathway in the yeast Schizosaccharomyces pombe.
• To identify specific cleavage sites within the precursor rRNA.
• To investigate the role of conserved sequences and small nucleolar RNA in rRNA maturation.

Main Methods:

• Primer extension analysis
• Nuclease protection assays
• Northern hybridization analyses
• Transcript mapping of transcribed spacer regions

Main Results:

• Six cleavage sites were identified in the 5' external transcribed spacer, upstream of mature 18S rRNA termini.
• Two of these sites and a site near the 18S termini show complementarity to conserved Box sequences in S. pombe U3 small nucleolar RNA.
• Internal transcribed spacers 1 and 2 appear to mature via initial endonuclease cleavage followed by processing to mature termini.
• Mature 5' termini of 25S rRNA are heterogeneous, similar to 5.8S rRNA, suggesting a structure-limiting role in the ribosome.

Conclusions:

• The major rRNA processing pathway for Schizosaccharomyces pombe has been elucidated.
• The findings support the model that rRNA maturation acts as a quality assurance mechanism.
• Conserved sequences and U3 small nucleolar RNA play roles in directing rRNA processing events.