Alternative splicing

Alternative splicing occurs when several splice donors and/or acceptors are eligible and facultative. This leads to transcripts having different splicing outcome and/or are unspliced. Alternative splicing is regulated by cellular and viral proteins which modulates locally the activity of splicing factors U1 and U2.
-It offers the opportunity to encode several proteins in few messengers, like for Adenoviridae and Retroviridae encoding up to 12 different peptides from one pre-mRNA.
-It is a way to regulate early and late expression for viruses like Papillomaviridae and maybe Orthomyxoviridae.
-Cellular unspliced mRNA cannot be exported out of the nucleus. Hepadnaviridae and Retroviridae have evolved proteins to export their unspliced genomic RNA.
-It is used by Herpesviridae as a potential anti-host defense mechanism. By inhibiting some host splicing factors, these viruses prevent the synthesis of key antiviral proteins like PML or STAT1.

Virus viral factor cellular factor Ref
ssDNA viruses
Anelloviridae
Circoviridae
Parvoviridae
dsDNA viruses
Adenoviridae 33k : expression of late proteins
Baculoviridae
Herpesviridae Unspliced RNA nuclear export
EBV- BM2
HCMV- UL69
HSV1- ICP27
EBV HCMV HSV-1
Papillomaviridae E2 activates cellular SR hnRNP A1 inhibit L1 mRNA expression
Polyomaviridae SF2 (SV40)
Reverse-transcribing viruses
Hepadnaviridae Capsid?: pg-RNA nuclear export
Retroviridae, Alpharetrovirus GAG genomic RNA nuclear export
Retroviridae, Lentivirus genomic RNA nuclear export
HIV-1 Rev
HTLV-1 Rex
HIV-1 HTLV-1
ss(-)RNA viruses
Bornaviridae
Orthomyxoviridae NS1 SF2