Journey to the Center of the Cell

The mechanisms used by pathogenic human viruses to cross the plasma membrane have been the focus of considerable attention. However, penetration into the cell cytoplasm is insufficient to permit the replication of many virus species. Specifically, all DNA viruses, except for pox viruses, as well as some viral families that bear RNA genomes, including retroviruses and influenza viruses, replicate in the nucleus. Only here can these viruses gain access to the cellular factors they require for the amplification and transcription of their genome and for the posttranscriptional processing of viral mRNA species. Therefore, these viruses not only have to cross the plasma membrane but must also traverse the cytoplasm and then enter the cell nucleus. In this review, I will briefly outline what is known about this process, using Human Immunodeficiency Virus Type 1 (HIV-1) and Adenovirus Type 2 (Ad2) as primary examples. A more comprehensive discussion is provided in a recent review by Whittaker et al.