The human 18S ribosomal RNA gene: evolution and stability

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genetics

Background:

• Ribosomal RNA (rRNA) genes are crucial for protein synthesis and are highly conserved across species.
• Understanding the structure and evolution of rRNA genes provides insights into fundamental biological processes.

Purpose of the Study:

• To determine the primary sequence and propose a secondary structure for the human 18S rRNA gene.
• To analyze the evolutionary conservation of the 18S rRNA gene, particularly in mammals.

Main Methods:

• Sequencing of the 1,870-base-pair human 18S rRNA gene.
• Comparative analysis with general mammalian rRNA structure to propose a secondary structure.
• Sequence divergence analysis between human and mouse 18S rRNA genes.

Main Results:

• The primary sequence of the human 18S rRNA gene was determined.
• A secondary structure model for the human 18S rRNA was proposed, based on conserved mammalian structures.
• Highly conserved regions (1,438 bases) and variable regions (432 bases) were identified.
• A remarkably low sequence divergence rate of 0.1% was observed between human and mouse 18S rRNA genes over ~80 million years.
• The 18S ribosomal DNA (rDNA) may represent one of the most highly conserved sequences known.

Conclusions:

• The basic secondary structure of small subunit rRNA is evolutionarily preserved through compensatory and neutral base changes.
• High sequence conservation in higher eukaryotes is likely maintained by strong selection and gene correction mechanisms.
• The 18S rRNA gene exhibits exceptional evolutionary stability, offering a valuable marker for evolutionary studies.