ABT1 (Activator of Basal Transcription 1) is a protein involved in regulating gene expression by initiating transcription. It functions as part of the RNA polymerase I (Pol I) machinery, which transcribes ribosomal RNA (rRNA) genes. ABT1 acts as a transcription factor, binding to specific promoter sequences of rRNA genes and recruiting other transcription factors along with the Pol I complex to facilitate rRNA production.