Separation of subcellular components and viruses by combined rate- and isopycnic-zonal centrifugation.

The re-isolation of trace anlOunts of virus added to tissue hOInogenates has been taken as a Inodel probleIll in the developIllent of high-resolution Illethods for separating particles. FroIll a review of data on these particles, it was found that, when sediIllentation rates are plotted against their banding or buoyant densities, IllOst viI'uses fall in a "window" which appears to be free of other particles. To exaIlline this concept experiIllentally, a technique for sequential rate-zonal and isopycnic-zonal centrifugation has been developed which allows this two-diIllensional separation to be Illade and visualized. By use of this so-called Sop SysteIll, trace quantities of T3 phage particles have been recovered and identified froIn rat liver, brain, and spleen hOlllogenates. The Inethod Inay be used to isolate trace quantities of virus-like particles that have occasionally been reported in hUInan tunlOrs.-Nat Cancer Inst Monogr 21: 253-283, 1966.