TFIIIR is an isoleucine tRNA

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• RNA polymerase III (Pol III) transcribes essential non-coding RNAs, including transfer RNAs (tRNAs).
• Pol III transcription initiation requires specific transcription factors (TFs).
• A unique TFIIIR component, previously identified in silkworm nuclear extracts, was known to be RNA-based.

Purpose of the Study:

• To identify the specific RNA molecule responsible for the transcription factor IIIR (TFIIIR) activity.
• To elucidate the role of this RNA component in promoter-specific transcription by silkworm RNA polymerase III.

Main Methods:

• Biochemical fractionation of silkworm nuclear extracts to isolate TFIIIR activity.
• Copurification studies to correlate TFIIIR activity with specific RNA species.
• In vitro transcription assays using purified TFIIIR components and synthetic RNA.
• Hybrid selection assays using antisense RNA probes to confirm RNA identity.

Main Results:

• Silkworm tRNA(IleIAU) was identified as the component responsible for TFIIIR activity.
• TFIIIR activity was reconstituted using synthetic silkworm tRNA(Ile).
• Antisense tRNA(IleIAU) specifically selected TFIIIR activity, confirming its identity.
• Other tRNA species did not exhibit TFIIIR activity, indicating high specificity.

Conclusions:

• Silkworm tRNA(IleIAU) is the essential RNA component of the transcription factor IIIR.
• This discovery reveals a novel function for tRNA as a direct regulator of RNA polymerase III transcription.
• The high specificity of TFIIIR for silkworm tRNA(IleIAU) highlights a unique regulatory mechanism in silkworm gene expression.