BIOCHEMISTRY OF INSECT VIRUSES 513 



amino acid composition of purified polyhedron and capsule protein from 



different insect viruses was carried out by Wellington (1951, 1954). The 

 results, which are summarized in Table II, reveal that all the inclusion body 

 proteins analyzed have a very similar amino acid composition, although some 

 are from nuclear polyhedra of lepidoptera, one from polyhedra of a hjnnen- 

 opteron {N. sertifer), and one from capsules of a lepidopteron (C. murinana) 

 that develop in the cytoplasm. However, comparing any two of these pro- 

 teins, significant differences (P < 0.01) can be found in the quantity of amino 

 acids. An analysis of the membranes of P. dispar polyhedra showed no 

 quahtative differences of the amino acids between them and the polyhedron 

 protein (Wyatt, 1950). 



Treatment of B. mori polyhedra with anhydrous methanol and dried 

 hydrogen chloride gas converts all carboxyl groups to methyl esters (111 

 groups) and the basic groups to hydrochlorides (67 groups) (DesnueUe and 

 Chang, 1945). No analyses are available of other kinds of inclusion bodies, 

 such as cytoplasmic polyhedra and those characteristic of the polyhedrosis of 

 Tipula paludosa (Meigen). 



III. Chemical Composition of Virus Particles 



Breindl and Jirovec (1936) were the first to report that P. dispar polyhedra 

 give a positive Feulgen reaction. As we know now, this is due to the DNA 

 content of the enclosed virus particles. Ultraviolet absorption spectra of 

 alkaline polyhedra solutions also revealed nucleic acid (Dannenberg, cited in 

 Bergold and Schramm, 1942), which was confirmed by chemical tests 

 but contain no uronic acid and no free carbohydrates (Tarasevich, 1946). 

 Quantitative determinations show 0.84 % DNA, but no RNA in B. mori 

 polyhedra (Gratia et at., 1945); 13 % DNA in purified virus particles of 

 B. mori; and 16 % in those of P. dispar (Bergold, 1947; Bergold and Pister, 

 1948a). Intensive analyses of purified suspensions of different viruses 

 causing nuclear polyhedroses gave no indication of RNA (Wyatt, 1952a, b). 

 A reinvestigation of highly purified B. mori virns particles revealed that 

 they consist of about 7.9 % DNA and 0.915 % P, of which only 87 % is 

 bound in the DNA (Table III) (Bergold and Wellington, 1954). This is in 

 good agreement with the ratio of DNA bases to total P (Wyatt, 1952b). The 

 remaining 13 % P could come from the surrounding virus membranes, which 

 contain about 0.45 % P. There is about half as much nondialyzable P in the 

 membranes as in the virus. The kind of bond is unknown. About 9 % DNA, 

 but again no RNA was found in a purified preparation of the rod-shaped 

 nuclear virus of Aporia crataegi L. (Krieg, 1956). Investigations of the N and 

 P content of different virus particles and virus membranes, summarized in 

 Tables I and III indicate that the virus membranes obtained by alkaline 



