RNA viruses, like bacteriophage MS2, are able to package their own genomes with high selectivity within a host cell, even though the host cell is packed full of other nucleic acids. The mechanisms behind this selectivity are not completely understood, but previous studies suggest that specific regions of the RNA–termed “packaging signals”–serve as recognition sites for the viral proteins as they assemble into capsids around the RNA. MS2 capsids are made up of two components: 89 dimers of the coat protein (CP) and 1 copy of the maturation protein (MP). Previous models of packaging selectivity in MS2 focus on the role of the coat proteins, as they are the major component of the capsid and are known to interact strongly with multiple stem loops in the RNA that act as packaging signals. However, the MP interacts directly with the RNA in mature virus particles and might therefore play a role in packaging selectivity. To test this hypothesis we introduce mutations into the MP gene, grow up virus particles, and then sequence the RNA that is packaged in them. By measuring the ratio of viral and host RNA in vivo, we determine the packaging selectivity. In this poster, I will discuss results and difficulties encountered thus far. Additionally, I will outline future experiments to better understand the role of CPs in packaging selectivity.