Authors

Discussion

Organisms in Kinetoplastida have evolved an unusual genome architecture that requires all pol II transcribed genes to be expressed constitutively, with expression levels for individual genes typically regulated post-transcriptionally or through gene arrays. Transcriptional start regions are denoted by histone variants and histone lysine acetylation, with a lack of specific transcription factor sites. However, the way chromatin marks are interpreted by the cell is not completely understood. Seven predicted bromodomain factors, the reader proteins for acetyl-lysine, were identified in the Leishmania mexicana genome. These were screened using Cas9-driven knockouts, implicating BDF1-5 to be essential in promastigotes. Using an inducible null mutant, we have characterised the dual bromodomain factor BDF5 to be essential for L. mexicana promastigotes and amastigotes. ChIP-seq assessment of BDF5 genomic distribution identified it to be enriched at transcriptional start sites. Using an optimised proximity proteomics and phosphoproteomics approach, XL-BioID, we defined the BDF5-proximal environment to be enriched for proteins essential for transcriptional activity. Following inducible deletion of BDF5, transcriptional activity was disrupted for all pol II transcription units, leading to generalised defect in gene expression. Our results identify the requirement for Leishmania cells to interpret histone acetylation marks for normal levels of gene expression with BDF5 acting analogously to a basal transcription factor.