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Discussion 



Ch.^rgaff : I am wondering about the composition of the mitotic preparations 

 which you have made in the presence of lead thioglycol, in this case without the 

 use of detergents, you presumably do not move very much of the mass. Do you 

 find lipids in the spindle preparations r 



MazL'\ : I feel certain that we do recover lipoproteins, but chiefly because of 

 our diflriculties in sedimenting the proteins of the dissolved mitotic apparatus by 

 procedures that gave good patterns with the product of the older method. 

 Obviously, your question cannot be answered until we have used chemical and 

 ultracentrifugal methods that are appropriate for studies of lipoproteins. 



Ch.arg.\ff: Dr. Murray and I studied the eftect of colchicine and its reversal 

 by inositol on the metaphase arrest. We got the impression that the mitotic 

 apparatus consisted in part of lipoprotein which after application of detergents 

 you wouldn't expect to find any more. The second question I have concerns the 

 state of the sulphur. Do you have any cysteine determinations on your prepara- 

 tions ? What form would the sulphhydrul exist in ? 



M.AZLA : Yes, we have found one cysteine per 18 000 units of molecular weight, 

 weight. This isn't very much, but neither is the mitotic apparatus very stable. 



Mitchell : Could you tell us more about the occurrence of the special proteins 

 of the mitotic apparatus during the resting phases of the cell ? I imagine that what 

 you said in the earlier part of your talk — that these proteins are probably always 

 present, or at least are present in the unfertilized egg — means that we do not have 

 to postulate the synthesis of a special supernumerary apparatus for division. 



M.AZi.^ : In the immunological studies it was found that the antigens charac- 

 teristic of the mitotic apparatus were present at all stages of early development 



