BIOCHEMISTRY OF INSECT VIRUSES 517 



virus particles isolated from the cytoplasmic polyhedra of Dasyckira pudi- 

 bunda L. revealed that all P could be accounted for as RNA, amounting to 

 about 7 % by weight of the virus (Krieg, 1956). According to unpubhshed 

 results of Markham and Xeros, the cytoplasmic polyhedra of Sphinx populi 

 L. also contain about 0.9 % RNA but no DNA (Xeros, 1956). The fact that 

 these virus particles have RNA instead of DNA is of great significance, sug- 

 gesting fundamental differences in the chemical structure and hereditary 

 mechanism between the rod-shaped nuclear and the spherical cytoplasmic 

 insect viruses. The difference in the type of nucleic acid is also of diagnostic 

 importance. It is interesting that the cytoplasmic noninclusion virus of T. 

 paludosa contains DNA (Williams and Smith, 1957). 



Spectrographic and analytical investigations have revealed that Fe (0.015 

 %) and Mg (0.33 %) are the only metals present in appreciable quantities in 

 virus particles of B. mori (Holoway and Bergold, 1953, 1955). It is probably 

 not advisable to interpret the significance of such small quantities, but it is 

 interesting that there are three times as much Fe and four times as much Mg 

 in the virus particles as in the surrounding polyhedron protein. 



Intensive investigations of the amino acid composition of several viruses 

 were carried out by Wellington (1951, 1954). The results, which are sum- 

 marized in Table VI, show that the five different polyhedron viruses and two 

 capsule viruses analyzed all have a similar pattern of amino acid composition 

 which differs markedly from the pattern of the surrounding inclusion body 

 proteins. The virus contains proportionally twice as much arginine and 

 serine, only half as much lysine and tyrosine, and shows a greater variabihty 

 than the inclusion body protein. There are significant differences between 

 any two viruses which tend to parallel the morphological classification rather 

 than the grouping based on nucleic acid analyses. For example, the two 

 morphologically similar capsule viruses of C. murinana and C. fumiferana do 

 not differ much in their amino acids, but vary considerably in their nucleic 

 acid composition; whereas the morphologically different viruses of B. mori, 

 M. disstria, and M. americanum are similar in their nucleic acid, but not in 

 their amino acids, with smaller differences between the two Malacosoma 

 viruses. However, the P. dispar virus appears to be different from aU others 

 with respect to amino and nucleic acid composition, as well as in morpholo- 

 gical characteristics. The chemical composition of the virus membranes was 

 analyzed in another investigation and compared with that of the virus and 

 polyhedron protein (see Table VII) (Bergold and Wellington, 1954). It 

 was found that the membranes dissolve completely in 0.01 M alkali but not 

 in alcohol, ether, or cold HCl of any concentration. Quantitative analyses of 

 acid hydrolyzates (6 N HCl, 16 hr., 110°C.) revealed that the virus membranes 

 contain more aspartic acid and much less arginine than the virus. The 

 amino acids account for only 57.8 % of the weight of the virus membranes, 



