Alternatively spliced hBRF variants function at different RNA polymerase III promoters

Area of Science:

• Molecular Biology
• Gene Transcription
• Biochemistry

Background:

• Yeast transcription factor IIIB (TFIIIB) is a single complex essential for all RNA polymerase III (pol III) genes.
• Human pol III promoters exhibit varied requirements for TFIIIB activity, unlike the conserved yeast system.
• A human homolog of yeast BRF was previously implicated in internal promoters (5S, VA1) but its role in external promoters (U6) remained uncertain.

Purpose of the Study:

• To investigate the distinct roles of human TFIIIB subunits in RNA polymerase III transcription.
• To identify and characterize alternatively spliced forms of human BRF (hBRF) involved in pol III transcription.
• To determine the specific hBRF variants required for transcription at different human pol III promoters.

Main Methods:

• Isolation and cloning of cDNAs encoding alternatively spliced human BRF variants.
• Complex formation analysis between cloned hBRFs and TATA-box binding protein (TBP).
• Immunopurification of complexes containing cloned hBRFs for functional assays at various pol III promoters.

Main Results:

• Two alternatively spliced forms of human BRF, hBRF1 and hBRF2, were identified that complex with TBP.
• hBRF1 was found to be essential for transcription at internal promoters: 5S, VA1, 7SL, and EBER2.
• A distinct variant, hBRF2, was specifically required for transcription at the external human U6 promoter.

Conclusions:

• Human RNA polymerase III transcription utilizes distinct TFIIIB complexes.
• Alternative splicing of BRF generates variants (hBRF1 and hBRF2) with specialized functions at different promoter types.
• This finding highlights promoter-specific regulation of pol III transcription in humans.