Figure 3.

(A) Left: Substrate RNA (32A) is processively degraded into product (10A; a GC hairpin with 10 adenine bases) by WT exosome as no intermediate degradation products are detected. Right: a single point mutation in the neck region (Rrp41 R67G) abolishes the processivity as intermediate degradation products appear during the reaction. (B) Fluorescence anisotropy binding curve of the neck mutant exosome (Rrp41 R67G) with the fluorescently labeled 32A RNA. The single point mutation results in a 1000-fold reduction of the affinity between the RNA and the enzyme (compare: Figure 2A).