Further purification and characterization of threadlike particles associated with the Citrus Tristeza disease

Abstract

Additional purification of threadlike particles (TLP) from leaves and bark of Egyptian sour lime, Citrus aurantifolia (Christm.) Swing., and bark of Palestinian sweet lime, C. limmetioides Tanaka, infected with Citrus Tristeza disease, was achieved by density gradient centrifugation in cesium chloride, after fixation with formaldehyde. A buoyant density of 1.328 g/cm 3 was determined by the use of two viral markers. The UV adsorption spectrum of TLP was typical of a nucleoprotein, and the 260:280 ratio of 1.21 indicated a nucleic acid content of ca 6%. TLP contained RNA but no DNA and a single protein species with a molecular weight of 25,000 ± 1000. TLP are helically constructed with a basic pitch of 37 + 2 Å and ten subunits in each turn of the basic helix. A molecular weight of 144 ± 23 × 10 6 for a particle with a normal length of 2000 nm was estimated. These properties of TLP, resembling those of other filamentous viruses, as well as their presence in infected tissues only, lend strength to the suggestion that TLP are the causal agent of the tristeza disease.