Fig 1: Selective interaction of TOP1MT with transcriptionally active nucleoids and POLRMT. (A, B) Cells expressing MY-TOP1MT stained with POLRMT antibodies (A) or expressing MY-TOP1MT, MY-TOP1MTY559F or MY stained with BrU antibodies following incubation with 2.5 mM BrU (B); corresponding images of YFP-specific fluorescence (middle right), antibody-specific fluorescence (right) and merged signals (middle left and left) are representative of the whole-cell population. Boxes in the overviews (left) indicate areas selected for 3-fold enlarged representation; arrows: MY-TOP1MT foci co-localizing with POLRMT or BrU; open arrowheads: MY-TOP1MT foci not co-localized with BrU. (C) Co-immunoprecipitation of TOP1MT or TOP1MTY559F with POLRMT. Lysates of untransfected cells or cells expressing MY, MY-TOP1MT or MY-TOP1MTY559F were subjected to YFP- (top) or POLRMT-directed (bottom) immunoprecipitation. Equivalent amounts of run through (left) and immune-precipitate (right) were probed with antibodies against YFP, TOP1MT, POLRMT or TFAM as indicated on the right margin. The result is representative of three identical experiments with similar result. (D) Exchange rate of MY-TOP1MT molecules at nucleoids analysed by fluorescence recovery after photo bleaching. Images of a selected mitochondrial segment acquired before and at the indicated time points after bleaching a selected MY-TOP1MT focus (arrows).