Figure 5. A small fraction of endogenous USP15 associates with polysomes. (A) USP15 co-fractionates with polysomes. HEK-293T cells were subject to gradient density centrifugation and fractions immunoblotted for the small ribosomal subunit protein RPS6, the soluble protein GAPDH and USP15. The A254nm profile was used to determine the fractions containing polysomes, free ribosomes and ribosomal subunits. (B) Dissociation of polysomes to 80S ribosomes shifts USP15 but not GAPDH within the density gradient. The experiment in (A) was repeated including a replicate sample that was treated with RNase for 1 min prior to gradient density centrifugation.