DNA compaction during intense transcription measured by electron microscope tomography

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Balbiani rings (BR) are large transcription sites in insect salivary glands.
• Understanding gene structure and DNA organization is crucial for gene regulation studies.

Purpose of the Study:

• To investigate the in situ DNA compaction ratio of hyperstimulated Balbiani ring genes in Chironomus tentans.
• To estimate the degree of nucleosome unfolding in actively transcribing genes.

Main Methods:

• Electron microscope tomography (EMT) was used to reconstruct thick sections of Chironomus tentans salivary glands.
• Six transcription loops of pilocarpine-hyperstimulated BR genes were analyzed at low resolution.
• Transcription unit length was measured in situ and compared to coding region DNA length.

Main Results:

• The average transcription unit length of BR genes was measured.
• The in situ DNA compaction ratio was estimated to be approximately 3-fold.
• This low compaction ratio indicates significant nucleosome unfolding.

Conclusions:

• Hyperstimulated Balbiani ring genes in Chironomus tentans exhibit a low DNA compaction ratio.
• The findings suggest a substantial degree of nucleosome unfolding in these actively transcribing genes.
• This provides insights into the structural organization of highly active genes.