RNA substrates are threaded through the internal channel of the core to Rrp44 by RNA helicase components of the nuclear TRAMP complex (Trf4-Air2-Mtr4 polyadenylation complex) or the cytoplasmic Ski (superkiller) complex. 
TRAMP
RNA substrates are threaded through the internal channel of the core to Rrp44 by RNA helicase components of the nuclear TRAMP complex (Trf4-Air2-Mtr4 polyadenylation complex) or the cytoplasmic Ski (superkiller) complex. 
Ski
Exosome substrate targeting: the long and short of it.The exosome ribonuclease complex functions in both the limited trimming of the 3'-ends of nuclear substrates during RNA processing events and the complete destruction of nuclear and cytoplasmic RNAs.  The two RNases of the eukaryotic exosome, Rrp44 (rRNA-processing protein 44) and Rrp6, are bound at either end of a catalytically inert cylindrical core.  Although the substrates of the exosome are known, it is not clear whether specific substrates are restricted to one or other pathway.  Data currently available support the model that processed substrates are targeted directly to the catalytic subunits, whereas at least some substrates that are directed towards discard pathways must be threaded through the exosome core.
exosome