These video files show our real-time cytotoxic assays. Video S1 shows real-time functional data of the 6_2G3 melanoma-specific patient derived antibody which was observed to kill melanoma cells. Video S2 shows the identical assays shown in Video S1 using a non-melanoma specific antibody derived from the same patient, as a negative control. In these assays, live tumor cells are labeled in green (live cell dye), U-937 monocytic cells are labeled in blue, and cell death is indicated by the incorporation of red (Ethidium homodimer-1 incorporation). Frames from these videos are also displayed in Figure 7 , B. The Multifaceted Poliovirus 2A Protease: Regulation of Gene Expression by Picornavirus Proteases After entry into animal cells, most viruses hijack essential components involved in gene expression. This is the case of poliovirus, which abrogates cellular translation soon after virus internalization. Abrogation is achieved by cleavage of both eIF4GI and eIF4GII by the viral protease 2A. Apart from the interference of poliovirus with cellular protein synthesis, other gene expression steps such as RNA and protein trafficking between nucleus and cytoplasm are also altered. Poliovirus 2A(pro) is capable of hydrolyzing components of the nuclear pore, thus preventing an efficient antiviral response by the host cell. Here, we compare in detail poliovirus 2A(pro) with other viral proteins (from picornaviruses and unrelated families) as regard to their activity on key host factors that control gene expression. It is possible that future analyses to determine the cellular proteins targeted by 2A(pro) will uncover other cellular functions ablated by poliovirus infection. Further understanding of the cellular proteins hydrolyzed by 2A(pro) will add further insight into the molecular mechanism by which poliovirus and other viruses interact with the host cell. A great variety of animal viruses encode for proteases that accomplish crucial functions during the biological cycle of the virus [1] . Usually, the main function of these proteases is to proteolyze viral polypeptide precursors to render mature viral proteins that form part of viral capsids or participate in virus vegetative processes [2] . Although both DNA and RNA viruses can encode proteases, the proteolytic tailoring of polypeptide precursors is most common among viruses with positive single-stranded RNA genomes, such as picornaviruses, flaviviruses, caliciviruses, and retroviruses [3] [4] [5] [6] [7] . This mechanism of gene expression by proteolytic processing serves to compress the genetic information of viruses in the limited space provided by the genome. In this manner, viruses reduce the genetic space occupied by 5 and 3 untranslated regions (UTRs), the signals devoted for mRNA transcription and to initiate translation are minimal, such that, for instance, in the case of picornaviruses or flaviviruses, only one 5 and 3 UTR is necessary for viral replication, transcription, translation, and morphogenesis, despite the fact that several viral proteins are synthesized by the infected cells. In addition, a number of polypeptide precursors may exhibit functions that differ from those present in their mature products. In the case of poliovirus (PV), eleven mature proteins are produced from a single translation initiation event, and at least two precursors, 2BC and 3CD, accomplish functions which are not present in their mature proteins. Taking together all these considerations, the "proteolytic strategy" provides the small RNA viruses with an advantageous and efficient mechanism for distribution of the genome to accomplish all the viral biological functions with the smaller genetic space.