Alternative splicing
Alternative splicing is a mechanism by which different proteins can be produced from a single gene by means of using alternative splicing sites to produce different mRNAs. It is found in various DNA, -ssRNA, and reverse transcribing viruses. Viruses may make use of alternative splicing solely to produce multiple proteins from a single pre-mRNA strand or for other specific purposes. For certain viruses, including the families "Orthomyxoviridae" and "Papillomaviridae", alternative splicing acts as a way to regulate early and late gene expression during different stages of infection. Herpesviruses use it as a potential anti-host defense mechanism to prevent synthesis of specific antiviral proteins. Furthermore, in addition to alternative splicing, because cellular unspliced RNA cannot be transported out of the nucleus, hepadnaviruses and retroviruses contain their own proteins for exporting their unspliced genomic RNA out of the nucleus.