FUNCTIONS OF NUCLEAR PHOSPHATASE 61 



one organic molecule to another. In considering the possible 

 functions of phosphatase in cell nuclei, we must bear in mind 

 both of these activities of alkaline phosphatase. It must also 

 be borne in mind that the results obtained with Drosophila sali- 

 vary chromosomes indicate that alkaline phosphatase is found 

 associated with all the genes, or at least with a very large num- 

 ber of quite diverse genes, so that its activity cannot be restricted 

 to any very specific function. 



If we consider the hydrolytic function of alkaline phosphatase 

 there are at least three possible functions for phosphatase in 

 nuclei. These are: 



1. A protective function. An active cell contains a number of vigorous 

 phosphorylating agents such as adenosine triphosphate and acetylphosphate. 

 Exposure of the genes to any of these substances might well be hazardous, 

 and it may be that the function of the alkaline phosphatase of the chromo- 

 somes is to protect the genes against the action of these phosphorylating 

 agents. 



2. A final stage in synthesis of a gene product may normally be dephos- 

 phorylation. For example, if we are to regard the typical gene products as 

 proteins, we must remember that it is quite possible that protein synthesis 

 involves the formation of a phospho-protein, and that the action of alka- 

 line phosphatase in the nuclei is to split off the phosphate residue from 

 the protein, and thus liberate an active product from an inactive precursor. 



It is of interest to reflect that the occurrence of phospho-proteins in 

 milk and in the yolk of eggs need not necessarily denote a special synthesis 

 of a phospho-protein in these instances. It may instead be an indication 

 of the suspension of a dephosphorylation process, which is normally car- 

 ried out when the function of the nucleus is to pass an active protein into 

 the cytoplasm. That is, by the suspension of dephosphorylation, it may 

 be that proteins which would otherwise participate in the chemical reac- 

 tions proceeding in cytoplasm are protected against such activity and thus 

 can be stored. 



3. A third possibility is that alkaline phosphatase is concerned in some 

 way with nucleic acid synthesis. Such a proposal has been made by several 

 authors. It is, however, far from clear in what way alkaline phosphatase 

 might be concerned. 



If we consider alkaline phosphatase as a phosphokinase, there 

 are at least two possibilities involved. The first of these is that 

 synthesis of phosphate esters may be a normal function of the 

 nucleus, and that the function of alkaline phosphatase is to trans- 

 fer phosphate groups from precursor substances to the specific 

 molecules which are involved in the activities of genes. An 

 alternative function is that alkaline phosphatase might serve as 



