Alkali-liberated granulosis virus of Trichoplusia ni: I. Density gradient purification of virus components and some of their in vitro chemical and physical properties

Abstract

Trichoplusia ni capsules were purified by a combination of differential and ratezonal centrifugation on 50 to 80% sucrose gradients. The virus was released and purified from the inclusion body protein by exposure to weak alkali and subsequent centrifugation on 10 to 40% sucrose gradients. Virus preparations maintained in 0.01 m phosphate buffer ( pH, 7.8) demonstrated 3 sedimenting forms on 10 to 40% sucrose gradients which were designated as A and B (with outer envelope) and Y (without outer envelope). The virus was unstable in 0.01 m phosphate buffer pH 7.8, and had a tendency to aggregate, and/or dissociate into the outer and inner membranes and a top fraction. The infection properties of each virus form and the top fraction were tested. Other buffers or additives did not change these phenomena. These virus forms and components were separated by a combination of sedimentations on 10 to 40% and 5 to 20% sucrose gradients and their ultrastructure confirmed by electron microscopy. Solutions containing virus forms A and B exhibited an E 260 E 280 of 1.26 and DNA and protein concentrations of 27.4 and 28.8 μg DNA/ E 260 and 105 and 109 μg protein/ E 260 for forms A and B, respectively. Preparations of the Y form contained 73.0 μg DNA/ E 260 and 258 μg protein/ E 260, but exhibited only 53% the ultraviolet extinction of virus forms A and B. Studies confirmed that the granulosis virus of Trichoplusia ni is ultrastructurally similar to other granuloses.