Bacteriophage MS2: Molecular Weight and Spatial Distribution of the Protein and RNA Components by Small-Angle Neutron Scattering and Virus Counting Structure

as a translation repressor of transcription of the MS2 replicase cistron. The A protein (or maturation protein) has been shown to be involved in attachment to the bacterial pilus, replication, RNA packing, and infectivity in vivo. The replicase and lysis proteins are involved in , 1986, 1990, 1991). From crystallographic analysis, the MS2 virion is thought to be comSmall-angle neutron scattering (SANS) has been used posed of 90 coat protein homo-dimers arranged in a to extend the structural characterization of the MS2 quasi-equivalent T ϭ 3 lattice to form the icosahedral phage by examining its physical characteristics in socapsid shell of the type described by Caspar and Klug lution. Specifically, the contrast variation technique (1962). In the capsid, coat protein dimers are thought was employed to determine the molecular weight of to adopt two possible noncovalent quasi-equivalent arthe individual components of the MS2 virion (protein rangements, A/B and C/C. The A and C subunits interact shell and genomic RNA) and the spatial relationship at the quasi 6-fold axes while the B-type subunits interof the genomic RNA to its protein shell. A consequence act at the 5-fold axes. Structurally, the primary differof this work was to evaluate a novel particle counting ence between these conformers lies in the position of instrument, the integrated virus detection system the FG loop region of the protein. ate a novel instrument, the integrated virus detection 1976). The MS2 coat protein is the primary structural system (IVDS). The IVDS instrument is not a traditional component of the MS2 protein shell. In addition to this particle counter of the type that is now being used for function, it binds to the MS2 operator site and acts virus or phage quantification. Rather, it is a specialized instrument that can accommodate the unique challenges associated with biological materials, such as *Correspondence: [email protected]