Fibrillar Systems in the Mitotic Apparatus 



Hans A. Went - and Daniel Mazia ^ 



Macromolecules are intimately associated with all phases of cell 

 function and, indeed, are absolutely indispensable for many. Some, 

 such as enzymes, can apparently perform properly as individual 

 molecules in vitro, although within a cell they may be coupled to 

 structural elements imparting rigorous spatial orientation to the 

 enzymes. Small amounts can be studied profitably by virtue of their 

 catalytic activity. Other macromolecules occur in highly oriented 

 aggregates forming specific subcellular structures such as chromo- 

 somes, chloroplasts, mitochondria, plasma membrane, nuclear en- 

 velope, and mitotic apparatus. The lack of easily measured activity 

 specific for these macromolecules frequently presents difficulties to 

 experimental elucidation of their function within the aggregates. 

 One of the first steps that must be taken to study a macromolecular 

 aggregate is to isolate it in quantity and disperse it into its con- 

 stituent molecular subunits in a uniform solution. A potential ob- 

 stacle arises when observations on a dispersed system are extra- 

 polated and applied as an explanation for the structure and function 

 of the intact, oriented aggregate. However, we will have to content 

 ourselves with this limitation pending improved experimental pro- 

 cedures. 



Many cells entering division construct an elaborate structure 

 whose unique function appears to be that of insuring equal dis- 

 tribution of the hereditary material to the daughter cells. The 

 modern term "mitotic apparatus" was applied to this structure by 

 Mazia and Dan (1952) and embraces both the achromatic and the 

 chromatic portions of the nuclear division figure as described by 

 Flemming (1882). The centrosomes, the spindle, and the asters 

 constitute the achromatic portion, and the chromatic portion is now 

 } 



^ This work was in part supported by University of California research funds. 

 ^ Department of Zoology, Washington State University, Pullman, Washington. 

 ^ Department of Zoology, University of California, Berkeley, Cahfornia. 



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