STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 51 



no components of chromosomes have yet been observed to be antigenic.^ 

 However, various cytoplasmic structures readily induce antibody production 

 and it would be quite desirable to have data on the cross-reactivity of the 

 chromosomal constituents with these antisera, both as an approach to 

 possible metabohc relationships with other cellular substances and to the 

 problem of possible contamination with cytoplasmic antigens. 



6. Properties of Isolated Mitotic Figures 



Preparations of fertilized frog eggs or sea urchin eggs, in which the cells 

 were dividing approximately synchronously, were homogenized in very cold 

 aqueous alcohol to prevent autolysis (Mazia and Dan, 1952). Intact mitotic 

 spindles could be isolated by differential centrifugation and further purified 

 with a detergent solution containing HgOg, which maintained the — S- — S — 

 linkages apparently essential to fiber formation. If the initial dispersal of 

 egg material is effected in the presence of ATP, subsequent purification with 

 detergents can be avoided. Isolated mitotic figures can be seen in Fig. 5. 



These structures can be isolated in all mitotic stages containing the spindle 

 and appear to consist of characteristic fibers containing embedded attached 

 chromosomes. During the distribution of chromosomes effected by mitosis, 

 the genetic material behaves quite passively. The chromosomes comprise a 

 very tiny portion of the total mass of the mitotic apparatus, which in the 

 fertihzed sea urchin egg approaches 12 % of the total protem of the cell. As 

 noted earHer, spindle protein contains about 2 % of adenine nucleotide in a 

 tightly bound form. 



Mazia (1957) has reported on the properties of the proteins of the spindle. 

 In the cell taken before division, there is a comparable mass of soluble 

 protein, which aggregates as the spindle forms and returns to a soluble form 

 as the mitotic apparatus disappears. Mazia (1956) has reviewed the bio- 

 chemistry and biophysics of cell division and has discussed the problem of 

 the origin and role of the spindle structures in some detail. 



7. Nuclear Sap 



Direct ultraviolet spectrophotometry of the nuclear fluid in which chromo- 

 somes are immersed has not revealed the characteristic absorption of nucleic 

 acid. This sap was removed from oocyte nuclei; analysis revealed a typical 



^ Two recent reports bearing on this problem can certainly be expected to stimulate a 

 careful exploration of this question. The first is the claim that isolated DNA is indeed 

 antigenic (Blix et al, 1954). The second is the study of Billingham et al. (1956), which 

 records the observations that the antigens important in the development of skin "trans- 

 plantation immunity" are confined to nuclei. Furthermore, the antigenic activity of 

 nuclei is unaffected by ribonuclease and by trypsin but is destroyed by treatment with 

 deoxyribonuclease. Isolated histone nucleates, after digestion by trypsin but not before, 

 were found to have perceptible immunizing power. 



