Resolution of human transcription factor TFIIIC into two functional components

Area of Science:

• Molecular Biology
• Gene Transcription
• Virology

Background:

• RNA polymerase III transcribes tRNA and adenovirus VA genes.
• Transcription requires transcription factors TFIIIB and TFIIIC.
• The TFIIIC fraction's precise composition was previously unclear.

Purpose of the Study:

• To elucidate the functional components of the TFIIIC transcription factor.
• To characterize the roles of individual TFIIIC components in VA1 gene transcription.

Main Methods:

• Fractionation of human cell extracts to isolate TFIIIC components.
• In vitro transcription assays to assess functional activity.
• DNase I footprinting to map protein-DNA interactions.
• Sedimentation analysis to determine component sizes.

Main Results:

• TFIIIC was separated into two functional components: TFIIIC1 and TFIIIC2.
• Both TFIIIC1 and TFIIIC2 are necessary for VA1 gene transcription.
• TFIIIC2 binds to the B block, and TFIIIC1 extends binding to the A block.
• TFIIIC1 is the limiting factor for VA1 transcription.
• TFIIIC2 is an ~18S complex, and TFIIIC1 is a ~9S complex.

Conclusions:

• TFIIIC is composed of at least two distinct functional subunits, TFIIIC1 and TFIIIC2.
• These subunits cooperate to mediate VA1 gene transcription by RNA polymerase III.
• The distinct binding properties and sedimentation behaviors confirm their unique identities.