A) Deletion of the N-terminal of Sen1 is lethal. A ∆sen1 strain (YDL2767) covered by an URA3-containing plasmid (pFL38) expressing wt Sen1 was transformed with a TRP1-plasmid (pFL39) carrying either the wt or the mutant versions of SEN1 indicated in the scheme on the left. After over-night growth in non-selective medium, cells were plated on minimal medium (CSM) containing 5-fluorootic acid (5-FOA) to select those that have lost the URA3 plasmid. The absence of growth in 5-FOA implies that the SEN1 version expressed in the TRP1-plasmid does not support viability. 