Trypanosoma brucei transcription activator for monoallelic surface coat expression

Trypanosoma brucei parasites undergo an iconic example of antigenic variation. To achieve expression of one and only one surface coat protein from a library of thousands of coat proteins they use specialised expression sites (ESs). ESs are only active in mammalian-infective life cycle stages and contain one variant surface glycoprotein (VSG) gene and several expression site associated genes (ESAGS). Each ES has a single promoter responsible for transcription of all genes in the ES. Extremely unusually for protein-coding genes, the polymerase used is RNA Polymerase I (Pol I) promoter and the active ES is found in a non-nucleolar, non-membrane bound, Pol I-containing nuclear sub-compartment. ESB1 is the first identified specific component of this compartment and we characterise the impact of ESB1 perturbation on the transcription of expression sites (ESs).