Soluble antigens of vaccinia-infected mammalian cells. 3. Relation of "early" and "late" proteins to virus structure.

The structural proteins of vaccinia virus can be divided into two classes on the basis of their times of synthesis in the infected cell. The production of one of these classes of proteins begins prior to the onset of viral deoxyribonucleic acid (DNA) replication. These are referred to as "early" proteins. Synthesis of the second class of structural proteins follows the onset of viral DNA replication; hence, the term "late" proteins for this class. We are able, by immunological procedures, to identify three "early" virus-structural proteins. These materials, when incorporated into virions, appear to be associated with the "core" of the virion and do not elicit production of virus-neutralizing antibody. It would seem, therefore, that those virus-structural proteins synthesized early in the course of infection act as internal components of the virion. The "late" proteins may be subdivided into two groups on the basis of certain physical properties and molecular weight differences. The first of these groups, comprised of at least two proteins, corresponds to the classical LS antigens and elicits production of neutralizing antibodies. These proteins, when incorporated into virions, are found only in the outer ("coat") fraction of the virion. The second group of "late" antigens, also comprised of two proteins, termed the G antigens, do not elicit synthesis of neutralizing antibody. One of these proteins is associated with the virus "core"; the other is found in the "coat" fraction of the virion and appears to occupy an intermediary, subsurface position. Procedures suitable for the isolation of the G antigens are described, in addition to the partial characterization of these antigens.