Factor-dependent transcription termination mechanisms are poorly understood. We determined a series of cryo-electron microscopy structures portraying the hexameric ATPase ρ on path to terminating NusA/NusG-modified elongation complexes. An open ρ ring contacts NusA, NusG, and multiple regions of RNA polymerase, trapping and locally unwinding proximal upstream DNA. NusA wedges into the ρ ring, initially sequestering RNA. Upon deflection of distal upstream DNA over the RNA polymerase Zinc-binding domain, NusA rotates underneath one capping ρ subunit, which subsequently captures RNA. Following detachment of NusG and clamp opening, RNA polymerase loses its grip on the RNA:DNA hybrid and is inactivated. Our structural and functional analyses suggest that ρ and other termination factors across life may utilize analogous strategies to allosterically trap transcription complexes in a moribund state.

Homologs of BT1 (the Brittle1 protein) are found to be phylogenetically related to the mitochondrial carrier family and appear to occur in both mono-and dicotyledonous plants. Whereas BT1 from cereals is probably involved in the transport of ADP-glucose, which is essential for starch metabolism in endosperm plastids, BT1 from a noncereal plant, Solanum tuberosum (StBT1), catalyzes an adenine nucleotide uniport when functionally integrated into the bacterial cytoplasmic membrane. Import studies into intact Escherichia coli cells harboring StBT1 revealed a narrow substrate spectrum with similar affinities for AMP, ADP, and ATP of about 300 -400 M. Transiently expressed StBT1-green fluorescent protein fusion protein in tobacco leaf protoplasts showed a plastidic localization of the StBT1. In vitro synthesized radioactively labeled StBT1 was targeted to the envelope membranes of isolated spinach chloroplasts. Furthermore, we showed by real time reverse transcription-PCR a ubiquitous expression pattern of the StBT1 in autotrophic and heterotrophic potato tissues. We therefore propose that StBT1 is a plastidic adenine nucleotide uniporter used to provide the cytosol and other compartments with adenine nucleotides exclusively synthesized inside plastids.

Highlights d CLK kinases are thermo-sensors reactive to subtle bodytemperature changes d Body temperature globally controls splicing and gene expression through CLKs d CLK homologs are evolutionarily adapted to diverse body/ growth temperatures d Wide functionality of CLKs: from TSD in reptiles to circadian biology in mammals