FIBRILLAR SYSTEMS IN THE MITOTIC APPARATUS 



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fraction contained, as the only antigens detectable, large amounts of 

 both the precursor- 1 and precursor-2 components. Undoubtedly 

 other protein species were present but eluded detection since the 

 antiserum did not contain antibodies specific for them. After the 

 yolk particles had been lysed, the residual solid matter was washed 

 and also extracted in 0.5M KCl. The resultant supernatant, termed 



Fig. 3. Intracellular distribution of the precursor-! and precursor-2 com- 

 ponents. SUP. I, SUP. II, and SUP. Ill refer to the original supernatant, the 

 yolk particles, and the two subsequent wash solutions, respectively. YPL rep- 

 resents the yolk-particle lysate, and EXT. LYP refers to the 0.5M KCl extract of 

 the structural material remaining after osmotic rupture of the yolk particles. 

 EXT. M&M indicates the 0.5M KCl extract of the mitochondria-microsome frac- 

 tion. Arrow 1 points to the precursor-! component band, and arrow 2 indi- 

 cates the position of the precursor-2 component band. It can be seen that 

 these two components were the main antigens detected in the extracts of the 

 mitochondria-microsome fraction and the lysed yolk-particle fraction. It would 

 appear that the precursor-! component is present as a "soluble" antigen within 

 the yolk particles as well as in the surrounding cytoplasm. 



the lysed yolk-particle extract, was immunochemically identical with 

 the microsome-mitochondria extract. These relationships can be 

 seen in Fig. 3. Both components of the mitotic apparatus have been 

 found in all fractions studied from the unfertilized egg. However, 

 two fractions, the lysed yolk-particle extract and the microsome- 

 mitochondria extract, yield solutions in which the precursor- 1 com- 



