140 ALEXANDER L. DOUNCE 



enzyme can easily be brought into aqueous solution and therefore should 

 be easily lost. This enzyme obviously must be one of general distribution. 

 Hogeboom and Schneider conclude that one manner in which the nucleus 

 might exert its effect on cytoplasm would be through formation of coen- 

 zyme I. This conception of coenzyme synthesis by nuclei, which was pre- 

 viously suggested by Brachet,^'^ may be true, but should be regarded with 

 considerable skepticism. In the first place, it has not been shown by Hoge- 

 boom and Schneider that DPN added to the homogenate can be quanti- 

 tatively recovered. In the second place, it is not likely that mitochondria 

 are permeable to DPN, although they contain this coenzyme. If all of the 

 DPN of the cell is synthesized in the nucleus, it is difficult to account for 

 intra-mitochondrial DPN. Finally, it is scarcely reasonable that genetic 

 effects due to the nucleus could be mediated by coenzyme synthesis, and 

 hence, even if DPN is synthesized entirely in the nucleus, this apparently 

 can only be a very special type of nuclear function. In order that genetic 

 effects should be passed from the nucleus to the cytoplasm, it seems neces- 

 sary to conclude that large and complicated molecules, such as nucleic acid 

 or protein or both, should likewise be able to pass from the nucleus to the 

 cytoplasm. 



The reader is referred to the references already cited for further infor- 

 mation concerning enzymes reported to be in the cell nucleus which have 

 not been considered here, and in particular to the table given by Lang^^^ 

 and to the papers of Mirsky et alP'^^ Another analysis of the situation in 

 regard to nuclear enzymes is given in a recent review by Hogeboom et al}^^ 



d. Enzymes of Nucleic Acid Synthesis. The fact that nuclear PNA thus 

 far has always shown a higher rate of incorporation of radioactive phos- 

 phate than cytoplasmic PNA indicates that enzymes involved in PNA 

 synthesis must be present within the cell nucleus. Since DNA is a chromo- 

 somal constituent, and since the best evidence indicates that DNA is 

 probably synthesized at the end of interphase,^" •^^^"'*^ it follows that en- 

 zymes concerned with DNA synthesis must also be present within the cell 

 nucleus. (Claims that DNA in some cases is not synthesized at the end of 

 interphase can be found in the literature.^'*-"^^^ 



e. Enzymes of Protein Synthesis. The fact that histone and residual 



1" J. Brachet, Nature 168, 205 (1951). 



138 ^ \Y Pollister and H. Ris, Cold Spring Harbor Symposia Quant. Biol. 12, 147 



(1947). 

 "9 H. Swift, Proc. Natl. Acad. Sci. U.S. 36, 643 (1950). 

 '"> H. Swift, Physiol. Zool. 23, 169 (1950). 



»' P. M. B. Walker and H. B. Yates, Proc. Roy. Soc. (London) B140, 274 (1952). 

 "2 J. Pasteels and L. Lison, Arch. biol. (Paris) 62, 1 (1950). 

 1" J. Pasteels and L. Lison, Compt. rend. 230, 780 (1950). 

 1" J. Fautrez and N. Fautrez-Firlefyn, Nature 172, 120 (1953). 



