172 MACROMOLECULAR COMPLEXES 



precursor-2 component in solutions of digitonin-isolated mitotic 

 apparatus? Experiments established that the precursor-1 component 

 was relatively insensitive to alkaline environments up to pH 10.5-11, 

 the conditions under which digitonin-isolated mitotic apparatus 

 could be put into solution, while the antigenic properties of the 

 precursor-2 component were nearly completely destroyed in this pH 

 range. Until further information is available, it will be necessary to 

 consider the precursor-2 component essential to the structural con- 

 tinuity of the mitotic figure. In no way does the existence of this 

 component necessitate any modification of the precursor concept, 

 for it is also found in the unfertilized egg. 



An important aspect of the precursor concept is the intracellular 

 localization of the precursor-1 component in the unfertilized egg, 

 which in turn may provide an insight into the sequence for its 

 mobilization into the mitotic apparatus. Absorption studies were 

 conducted, using the particulate fraction, which is arbitrarily de- 

 fined as everything that can be sedimented at 60,000 g for 30 min- 

 utes from a homogenate of ethanol-preserved eggs. Extraction of 

 the particulate fraction by various procedures, and its subsequent 

 use to absorb antiserum, revealed that tenaciously associated with 

 the particulate fraction was an antigen that could combine specif- 

 ically with the antibodies homologous for the precursor-1 compo- 

 nent. Evidently the precursor-1 component occurs in an insoluble 

 form in addition to the readily extractable form, which will be re- 

 ferred to as the "soluble" form. 



Attention was then directed toward living material, for this would 

 lend itself more favorably to critical fractionation procedures neces- 

 sary to resolve the intracellular distribution of the "precursor" com- 

 ponents. Living, unfertilized eggs were gently dispersed in isotonic 

 dextrose medium in a manner that avoided disrupting the yolk 

 particles. The resultant suspension was then centrifugally fraction- 

 ated, roughly into three fractions : the volk particles, the microsome- 

 mitochondria fraction, and the supernatant to the microsome-mito- 

 chondria fraction. The yolk particles, after careful washing, were 

 osmotically lysed and the contents analvzed by gel-diffusion meth- 

 ods. Numerous antigens were present, including the precursor-1 

 and precursor-2 components. The supernatant was qualitatively 

 very similar to the yolk-particle lysate. The situation with the 

 microsome-mitochondria fraction, on the other hand, was verv dif- 

 ferent. This had been extracted with 0.5M KCl, and the soluble 



