PPD: A Manually Curated Database for Experimentally Verified Prokaryotic Promoters

•Promoter plays a key role in gene transcription regulation.•We presented a database PPD, which collected the experimentally validated promoters in prokaryotes.•PPD recorded 129,148 promoters across 63 prokaryotic species.•PPD provided an online genome browser for the visualization of the resources of prokaryotic promoter.•PPD might be a novel resource for the study of prokaryotic gene transcription.