(A) Trypanosomes proliferating in the mammalian bloodstream change into a non-proliferative form that is capable of transferring into a tsetse fly. All bloodstream trypanosomes have a dense surface VSG coat. (B) Trypanosomes express VSG proteins from a VSG expression site at a chromosome end (black triangles). The VSG expression sites include expression site associated genes (ESAGs; yellow boxes) as well as the telomeric VSG genes (red box). In the top panel, VSG1 is being expressed, with transcription (green arrow) proceeding from a promoter (white flag). Batram et al. found that inducing parasites to express a different VSG—labelled here as VSG 2 (blue box)—from another genomic location (black flag) results in a repressive gradient silencing the active expression site (red arrow). This not only silences VSG 1, but also reduces the expression of ESAGs near VSG 1.