D) A yeast one-hybrid screening strategy to identify proteins binding to the ub-HS-motif. Three copies of the ub-HS4-motif (F7) were cloned upstream of a minimal promoter followed by a HIS3 reporter-gene and integrated at the URA3 locus. A yeast cDNA library with N-terminally fused Gal4-AD was used to screen for survival on media lacking histidine and multiple plasmids coding for 4 different genes were recovered (bottom). 