Table 3 . Exosome and associated proteins involved in 3′ to 5′ degradation of RNAs.

Component	Features	Reference
Core exosome	Six RNasePH domain proteins (no active sites) Rrp41, Rrp42, Rrp43, Rrp45, Rrp46, Mtr3	Lykke-Andersen et al. (2011)
	3 RNA-binding subunits (Rrp4, Rrp40, Csl4)
	One catalytic subunit, Rrp44, with both endo and exo active sites
	Functions in both RNA processing and degradation in cytoplasm and nucleus
Cytoplasmic cofactors
Ski7	Binds Csl4 subunit of coreRequired for 3′ to 5′ decay of mRNAsGTPase domain required for non-stop decayInteracts with Ski2/Ski3/Ski8 complex	Van Hoof et al. (2000b, 2002); Wang et al. (2005)
Ski2/Ski3/Ski8 complex	Required for 3′ to 5′ mRNA decaySki2 is member of ATPase RNA helicase familySki8 is WD40 proteinSki3 may function as scaffold	Anderson and Parker (1998); Brown et al. (2000); Araki et al. (2001); Wang et al. (2005)
Nuclear cofactors
Rrp6	3′ to 5′ exonuclease of RNAseD family	Butler and Mitchell (2011)
	Associated with nuclear exosome
	Required for RNA processing and decay of RNAs in the nucleus
	Functions in retention of aberrant mRNAs at sites of transcription
Rrp47 (Lrp1)	RNA-binding protein	Butler and Mitchell (2011)
	Required for RNA processing and nuclear RNA decay
	Associated with nuclear exosome
Mpp6	RNA-binding protein	Milligan et al. (2008)
	Associated with nuclear exosome
	Required for RNA processing and nuclear RNA decay
Tramp complexes (Trf4 or Trf5)	Consist of Mtr4 with 1 noncanonical poly(A) polymerase (Trf4 or Trf5) and 1 RNA-binding protein (Air1 or Air2)Required for several RNA-processing and nuclear RNA decay pathwaysCan promote processing/degradation in poly(A)-dependent and -independent manners by recruiting exosome to substrates	Houseley and Tollervey (2006); San Paolo et al. (2009); Butler and Mitchell (2011)