Rrn7

Rrn7 is a protein component of the RNA polymerase I transcription machinery in budding yeast. It is part of the core factor (CF) that works with Rrn6 to facilitate transcription of ribosomal RNA (rRNA) genes. In Saccharomyces cerevisiae, Rrn7p forms a heterodimer with Rrn6p and, together with other initiation factors, helps recruit RNA polymerase I to the rDNA promoter and promote the assembly of the transcription initiation complex.

Function and role

Rrn7p contributes to promoter recognition and initiation of rRNA transcription. It interacts with Rrn6p and with elements of the Pol I initiation machinery, aiding the proper positioning of RNA polymerase I at the rDNA promoter. The CF complex, including Rrn7p, is localized to the nucleolus, consistent with its role in ribosome biogenesis and high levels of rRNA synthesis during growth.

Biological significance

Disruption or impairment of RRN7 reduces rRNA synthesis and leads to growth defects, underscoring its essential role in efficient ribosome production and cell proliferation under standard conditions. The protein is thought to be constitutively expressed, with activity linked to cellular needs for ribosome biogenesis.

Evolution and broader context

Rrn7p has homologs in other fungal species, where the core factor is similarly involved in RNA polymerase I transcription. The Core Factor–Rrn7/Rrn6 module is part of a conserved mechanism for Pol I transcription that, in higher eukaryotes, is related to SL1-like complexes that coordinate rRNA gene transcription.

Overall, Rrn7 serves as a key subunit of the Pol I transcription initiation apparatus in yeast, contributing to the regulation of ribosomal RNA production and cellular growth.