Tsetse fly rDNA: an analysis of structure and sequence

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• Ribosomal DNA (rDNA) organization is crucial for eukaryotic gene expression and evolution.
• The tsetse fly (Glossina morsitans morsitans) genome is incompletely understood, particularly its rDNA structure.

Purpose of the Study:

• To construct a genomic library of Glossina morsitans morsitans.
• To isolate and characterize a complete rDNA unit from this tsetse fly species.
• To compare its rDNA organization with other higher eukaryotes, focusing on the intergenic spacer, external transcribed spacer (ETS), and 18S gene regions.

Main Methods:

• Construction of a genomic library using phage vector EMBL 4.
• Isolation of rDNA unit using a Drosophila melanogaster rDNA clone as a probe.
• DNA sequencing of spacer subrepeats, ETS, and the initial part of the 18S gene.
• S1 mapping to determine the 45S precursor RNA promoter location.
• Sequence alignment and homology comparisons with other eukaryotic rDNA sequences.

Main Results:

• A complete rDNA unit of Glossina morsitans morsitans was isolated and characterized.
• The rDNA organization is typical of higher eukaryotes, featuring an intergenic spacer with subrepeats.
• The 45S precursor RNA promoter was atypically located within the last subrepeat, extending into the ETS.
• The ETS sequence showed complete divergence from other higher eukaryotes, with limited homology to Drosophila species.
• Key conserved sequences, including the G at -16 and the NTS-18S gene junction, displayed significant alterations.

Conclusions:

• The Glossina morsitans morsitans rDNA unit exhibits unique features, particularly in promoter localization and ETS sequence divergence.
• These findings suggest rapid evolutionary changes within the rDNA family, necessitating functional adjustments.
• The study highlights the dynamic nature of rDNA evolution and its implications for gene regulation and retention.