Viruses are small obligate intracellular parasites and are inert outside the host cell. A fully assembled infectious virus is called a virion, and is composed of a nucleic acid (RNA or DNA) and proteins encoded by this genome. The nucleic acid of the virus contains all the information needed to produce new viruses by interacting with host cells. This information includes how to make new viral particles and accessory proteins, as well as how to redirect the host cell machinery for reproduction of viruses. The structure of the virion is an indicator of the viral requirements during its replication cycle.
Viruses range in size from less than 100 nanometers to several hundred nanometers in diameter. They display a wide diversity of shapes and sizes, known as morphologies; these varied structures reflect the efficiency and stability constraints faced by the virus. The viral genome is packaged inside a protein coat along with some viral proteins to avoid degradation by nucleases. This protective coat is called the capsid. The capsids are made of multiple copies of a limited number of protein species, which assemble in large numbers to form a continuous three-dimensional structure. This three-dimensional structure can be arranged such that the proteins are wrapped around a helical filament of nucleic acid or can take on an icosahedral morphology, a shape characteristic of the nucleocapsids of many 'spherical' viruses.
Many viruses encode relatively few structural protein species, as well as a few accessory proteins that participate in the replication of the viral genome. There are some viruses with proteins, most of which participate in replication, but are not packaged into the virion. Additionally, the capsids of some virus types are surrounded by extra envelope; this envelope is a protein-rich lipid membrane bilayer acquired in part from the host cell during budding. Several classes of proteins are associated with virus envelopes. Virus encoded matrix proteins link the envelope to the core of the particle; glycoproteins are responsible for receptor recognition and binding. Thus, in addition to virus-specified envelope proteins, viruses may also carry some host cell proteins as integral constituents of the viral envelope.
Creative Biomart provides recombinant proteins of several sources, grades and formulations to help you for virus research applications.