Table 3.

Host shutoff mechanisms in influenza A virus.

Level of Regulation	Viral Protein	Molecular Activity	Result	Interacting Cellular Proteins
Transcription	RdRP (PA, PB1, PB2)	Ubiquitination and degradation of large subunit of RNA Pol II	Transcription inhibition	RNA Polymerase II
RNA processing	NS1	Inhibition of mRNA 3′ end cleavage by CPSF and PABPN stimulation of poly(A) addition; interaction with nuclear mRNA export machinery	Inhibition of poly(A) tail addition and nuclear export of mRNA	CPSF30
				PABPN
				Nuclear export proteins (NXF1, p15, Rae1, E1B-AP5, Nup98)
RNA stability	PA-X	RNA endonuclease	Degradation of host mRNA and ncRNAs; nuclear relocalization of PABPC	Unknown