Drug Repurposing: Tolfenamic Acid Inactivates PrbP, a Transcriptional Accessory Protein in .

CLIBASIA_01510, PrbP, is a predicted RNA polymerase binding protein in . PrbP was found to regulate expression of a small subset of ribosomal genes through interactions with the β-subunit of the RNA polymerase and a short, specific sequence on the promoter region. Molecular screening assays were performed to identify small molecules that interact with PrbP . Chemical hits were analyzed for therapeutic efficacy against via an infected leaf assay, where the transcriptional activity of was found to decrease significantly after exposure to tolfenamic acid. Similarly, tolfenamic acid was found to inhibit infection in highly symptomatic citrus seedlings. Our results indicate that PrbP is an important transcriptional regulator for survival of , and the chemicals identified by molecular screening assays could be used as a therapeutic treatment for huanglongbing disease.