Role of RNA structure and protein factors in the control of HIV-1 splicing

Alternative splicing plays a key role in the production of numerous proteins by complex lentiviruses such as HIV-1. The study of HIV-1 RNA splicing has provided useful information not only about the physiology of the virus, but also about the general mechanisms that regulate mammalian pre-mRNA alternative splicing. Like all retroviruses, a fraction of HIV-1 transcripts remains intact to serve as genomic RNA and to code for Gag and Gag-Pol protein precursors. In addition, splicing is important for controlling the production of some viral proteins, which could otherwise have a negative effect on the infected cell. Here, we summarize how the utilization of HIV-1 splicing sites is limited by the binding of nuclear factors to cis-acting silencer elements, taking into account the role of RNA secondary structure in these mechanisms. We also describe how the poorly efficient HIV-1 acceptor sites are nevertheless activated by serine/arginine-rich proteins. Finally, we discuss how nuclear factors that interact with both the transcription and splicing machineries also participate in the control of HIV-1 RNA splicing.