Transcription, splicing and transport of retroviral RNA
Tina Lenasi, Xavier Contreras, and B. Matija Peterlin
from: Retroviruses: Molecular Biology, Genomics and Pathogenesis (Edited by: Reinhard Kurth and Norbert Bannert). Caister Academic Press, U.K. (2010)
Studies of retroviruses have contributed greatly to our understanding of mechanisms that regulate eukaryotic gene expression. They include transcription, processing of nascent transcripts and transport of mRNA species from the nucleus to the cytoplasm. For example, analyses of viral promoters and enhancers revealed important aspects of initiation and elongation of transcription by RNA polymerase II. Sites of integration further emphasised contributions of chromatin and distal interactions between cis-acting sequences to the expression of viral genes and those of nearby oncogenes that lead to the transformation of target cells. At the level of DNA, they also introduced the concept of transcriptional interference for the silencing of viral 3' long terminal repeats, where their transcription terminates and nascent transcripts become polyadenylated. Next, studies of their complex splicing patterns revealed suboptimal splice donor and acceptor sites, splicing enhancers and silencers, as well as the competition between splicing and export of incompletely spliced retroviral mRNA species from the nucleus to the cytoplasm. There, they defined RNA and protein export mechanisms for cellular and viral macromolecules. Finally, current studies of the silencing of retroviral genomes promise to elucidate mechanism for turning on and off the expression of eukaryotic genes. Of all mammalian retroviruses, HIV has been studied the most and forms the basis of this chapter. However, lessons learned from this primate lentivirus inform all other retroviruses read more ...