BIOCHEMISTRY OF INSECT VIRUSES 507 



healthy ones (3.4 %); this is probably due to an increase of a protem com- 

 ponent with a sedimentation constant of 6.2 Svedberg (Bergold and Friedrich- 

 Freksa, 1947). About 7 % of the dry weight of infected B. mori larvae consists 

 of virus and polyhedra, which contain 2.5 % of the total P, 13 % of the 

 nucleo-protein P, and 10.6 % of the acid-soluble residual fraction P. The 

 total N of the diseased larvae is increased and the N of the virus nucleoprotein 

 forms 24 % of the N protein fraction. Polyhedron-diseased B. mori larvae 

 are deficient in P, but not in N (Tarasevich, 1952). In diseased larvae the 

 amount of P (chiefly the acid soluble components) is increased. The increase 

 of protein fraction is less than in the other fractions. Application of diamino- 

 purine and 4-aminopterine increased the number of polyhedrosis cases and 

 the P content of the protein fraction; whereas dinitrophenol, hydroxylamine, 

 acriduie, and aminomethylphosphoric acid boosted the P content of fat 

 tissue (Tarasevich, 1953). The amount of total nucleic acid and protein in 

 the fat body and body fluid is also increased in the later stages of nuclear 

 polyhedrosis oiB. mori larvae (Shigematsu and Takesliita, 1958). The activity 

 of tyrosinase in diseased larvae is only 20 % of that of healthy ones, and in 

 diseased larvae the amount of DNA is increased and that of RNA is decreased 

 (Tarasevich, 1954). 



The uptake of P^^ mto polyhedra from a standard dose of 0.6 /xC/larva 

 depends on the time elapsing after uifection with the virus before the mjec- 

 tion of P^^. If the interval is three days the amount (about 22 c.p.m./mg. 

 polyhedra) is three times as high as with an interval of one day (Yamafuji and 

 Omura, 1954). Polyhedral bodies obtained from dead B. rnori that were pre- 

 viously injected with C^*-labeled alanine and glycine (about 10 //.C/larva) 

 show an activity of about 1300 c.p.m./mg. However, virus particles isolated 

 from such polyhedra have 3800 c.p.m./mg. To explain tliis, one can assume 

 preferential incorporation of C^^ into the virus particles, or that polyhedra 

 develop later than the virus particles (Bergold, 1954). The rate of incorpora- 

 tion of glycine-C^* mto blood protein is not different m healthy and diseased 

 B. mori larvae (Faulkner, mipublished), although mjection of C^^-labeled 

 alanine and glycme (about 10 /xC per larva) appears to uiliibit somewhat the 

 virus multiplication, enabling the larvae to develop to adults (Bergold, 1954). 



II. Physicochemical Properties and Chemical Composition of 

 Inclusion Bodies 



A. Physicochemical Properties 

 Nuclear and cytoplasmic polyhedroses and granuloses are characterized by 

 the formation of the so-called inclusion bodies. Two main types can be dis- 

 tinguished: regular- or irregular- shaped polyhedra, which are about 0.5-15 jjl 

 in diameter, and ellipsoidal capsules with dimensions of about 200 X 500 lafx. 

 Bolle (1893) was the first to investigate polyhedra; he found that they are 



