Dispersed 5S RNA genes in N. crassa: structure, expression and evolution

Area of Science:

• Molecular Biology
• Genetics
• Eukaryotic Gene Organization

Background:

• Eukaryotic 5S ribosomal RNA (rRNA) genes exhibit diverse genomic organization across species.
• Understanding gene arrangement and sequence variation is crucial for deciphering gene regulation and evolution.

Purpose of the Study:

• To characterize the genomic organization and sequence diversity of 5S RNA genes in the fungus Neurospora crassa.
• To investigate the relationship between 5S gene sequences and the resulting 5S RNA molecules.
• To explore the evolutionary conservation of 5S RNA secondary structure.

Main Methods:

• DNA hybridization techniques to assess gene copy number and distribution.
• Cloning and sequencing of 5S DNA fragments.
• Analysis of 5S RNA sequences and comparison with gene sequences.
• Comparative sequence analysis with Saccharomyces cerevisiae 5S RNA.

Main Results:

• Neurospora crassa 5S genes are not tandemly arranged or tightly clustered, hybridizing to numerous DNA fragments.
• Approximately 100 copies of 5S genes exist, with individual clones containing single genes.
• Sequencing revealed multiple types of 5S genes (alpha, beta, beta', gamma, delta) with varying sequence divergence.
• Analysis identified a predominant 5S RNA species matching the alpha-type gene, along with minor species corresponding to other gene types.
• Nucleotide substitution patterns suggest conserved in vivo secondary structure of Neurospora 5S RNA.

Conclusions:

• The dispersed genomic organization of 5S genes in N. crassa contrasts with other eukaryotes.
• Sequence heterogeneity among 5S genes coexists with a dominant expressed form.
• Evidence supports the conservation of a specific 5S RNA secondary structure in vivo.