δ Agent: Association of δ Antigen with Hepatitis B Surface Antigen and RNA in Serum of δ -Infected Chimpanzees

The hepatitis B virus-associated β antigen was found in the serum of experimentally infected chimpanzees as an internal component of a discrete subpopulation of hepatitis B surface antigen (HBsAg) particles. The 35- to 37-nm particles banded in CsCl at 1.24-1.25 g/cm3 and sedimented with a mobility intermediate between that of the hepatitis B virion and that of the 22-nm form of HBsAg. The particles contained only indistinct internal structure by electron microscopy and were not unique to δ agent infection, similar particles without δ -antigen activity being observed in the preinfection serum of HBsAg carrier chimpanzees. A small RNA (Mr,5× 105) was temporally associted with δ antigen in the serum of infected chimpanzees and copurified with the δ -antigen-associated particles. This RNA is smaller than the genomes of known RNA viruses but larger than the viroids of higher plants.