362 



ERWIN CHARGAFF 



TABLE XIV 



Dissociation of Nucleohistone in Salt Solutions, after a Single 

 Treatment with Chloroform 



gel, whereas a similar treatment in salt solutions of increasing strength 

 results in the proportionate detachment of increasing quantities of nucleic 

 acid. This is illustrated in Table XIV,* which is based on the experiments of 

 Ciampton et a/.*" 



For details of the procedures the original papers^^*' ^*' should be con- 

 sulted. Full data on two abbreviated fractionation runs with calf thymus 

 nucleohistone, in which only three fractions were collected, are given in 

 Table XV P' 



Nucleohistone preparation N-NH was isolated, and precipitated at 0.15 M NaCl 

 concentration, as described in Section II.3.a.(l); preparation R-NH was isolated 

 similarly, but from a solution that had first been exposed to M NaCl. Solutions of 

 these preparations in distilled water (previously adjusted to pH 7), containing about 

 90 Mg- P per cc, were mixed with an equal volume of 1.3 M NaCI solution and, after 

 an interval of 30 minutes, treated in a high-speed mixer with one-half volume of 

 chloroform- octanol (9:1) for 2 minutes. From the supernatant fluids, obtained by 

 centrifugation (15 minutes, 2000 X g), the sodium nucleate fractions l-I and 2-1 

 (Table XV) were isolated as described in Section III.2.C. The sedimented gels were 

 reextracted, as described above, first with portions of 0.9 M NaCl equal to one-half 

 of the volume of nucleohistone solution (fractions l-II and 2-II) and then with 2.6 M 

 NaCl (fractions l-lll and 2-III). The results are shown in Table XV. The deoxy- 

 ribose content of the fractions varied from 95 to 100% of that of a standard prepara- 

 tion; protein was absent from all preparations. 



The results of seven similar fractionation experiments are shown in Fig. 

 4 in graphic form. This diagram contrasts the molar sums of adenine and 

 thymine found in each significant fraction with the corresponding sums of 

 guanine and cytosine. It will be noticed that the gradual extraction of the 

 nucleohistone with salt solutions of increasing strength yields a series of 

 nucleic acid fractions with diminishing concentrations of guanine and 

 cytosine and rising concentrations of adenine and thymine. But what should 

 be emphasized is that in all fractions the equimolarity of each pair of con- 



