STORAGE OF RESERVES 7-6 



This gives a measure of the total basophily, presumably the total 

 amount of nucleoprotein (which is principally ribose nucleoprotein 

 for the desoxyribose nucleoprotein makes up only a small fraction 

 of the total nucleoprotein) plus the metaphosphate. Since metaphos- 

 phate retains the dye more effectively than the nucleoprotein (it is 

 not removed by a short exposure to 1 per cent sulphuric acid), a 

 rough estimate of the metaphosphate fraction is achieved by deter- 

 mining the total basophily and subtracting the fraction of dye re- 

 moved by washing with 1 per cent sulphuric acid. The nucleopro- 

 tein stains blue and the metaphosphate red, so it is possible to get 

 some idea of the relative amounts by direct observation of the stained 

 cells. Cells grown in media deficient in nitrogen but supplied with 

 a maximum of all the other necessary ingredients show a marked 

 diminution in basophily. Ordinarily, the yeast cell contains so much 

 reserve ribose nucleoprotein in the cytoplasm and this substance 

 has such an affinity for basic dyes that attempts to use a stain like 

 aceto -orcein or methylene blue result in over-staining the entire 

 cell. However, in cells starved for nitrogen, aceto -orcein may dif- 

 ferentiate the heterochromatin in the centrosome very well. In the 

 actively growing cell, the ribose nucleoprotein is generally dispersed 

 throughout the cytoplasm; in the nondividing cell, it accumulates in 

 the mitochondria forming the cytoplasmic granules. The total 

 amount of ribose nucleic acid in the yeast cell varies, probably from 

 1 to 5 per cent of the dry weight, so the ribose nucleoprotein may 

 vary roughly between about 5 to 25 per cent of the dried weight. 

 Ribose nucleoprotein is readily dissolved by dilute sodium hydrox- 

 ide while desoxyribose nucleoprotein is not. This is the basis of 

 heterochromatin stain. 



THE FEULGEN-POSITIVE HETEROCHROMATIN 

 IN THE CENTROSOME 



Under various different conditions of the cell with regard to its 

 stored reserves about the same amount of basophilic (desoxyribose?) 

 nucleoprotein, as far as can be judged by microscopic observation, 

 appears in the centrosome, when one uses the heterochromatin stain 

 (extract in dilute alkali and stain with dilute toluidine blue). This 

 suggests that the centrosome is one of the structures which is rela- 

 tively independent of variations in the storage of other reserves. 

 The chromosomes are too delicate to stain, so we have no informa- 

 tion on the constancy of their basic protein. However, we assume 

 that they are present at all times and that the heterochromatin along 

 with the chromosomes forms part of the basic or "skeletal" structure 

 of the cell relatively unaffected by the storage of reserve. Von Euler 

 and Hahn (1947) have shown that bakers' yeast contains about 7 per 

 cent ribose nucleic acid and 0.3 per cent desoxyribose nucleic acid. 



