Enzymic Formation of Deoxyribonucleic Acid from 

 Ribonucleotides 



Peter Reichard 



Department of Chemistry /, Karolinska histitutet, 

 Stockholm, Sweden 



The work of Romberg and his associates [i] has estabhshed that 

 DNA* is formed enzymically through the polymerization of deoxvribonu- 

 cleoside triphosphates. It is thus evident that cells which carry out a 

 rapid synthesis of DNA require a constant supply of these compounds, 

 and the biological source of the deoxyribonucleotides becomes of major 

 importance. 



Earlier /;/ vivo experiments [2, 3] made it very likelv that deoxvribosvl 

 compounds in many different types of cells are formed through a direct 

 reduction of the corresponding ribosyl compounds. More recently it was 

 possible to demonstrate such conversions with enzvmes from chick embrvos 

 and Escherichia co/i, and it was then found that this reduction took place 

 at the diphosphate level, e.g. deoxycytidine diphosphate was formed from 

 cytidine diphosphate [4, 5]. 



Here I will describe experiments in which the enzymes catalyzing the 

 reduction of ribonucleotides are coupled with the enzymes synthesizing 

 DNA from deoxyribonucleotides. Thus in these experiments we studied 

 the over-all reaction sequence leading from ribonucleotides to the syn- 

 thesis of DNA. This work was carried out during a recent visit to the 

 Department of Pharmacology, Yale University, New Haven, U.S.A., in 

 collaboration with Drs. Z. N. and E. S. Canellakis. 



One major purpose of our investigation was to study possible regulatory 

 mechanisms during in vitro DNA synthesis. The reduction of a ribotide 

 to the corresponding deoxyribotide represents the first step in a reaction 

 sequence which ultimately results in the synthesis of DNA. All the pre- 

 ceding enzyme reactions leading to the formation of the ribotide can be 



* Abbreviations used: DX.A, deoxyribonucleic acid; CMP, CDP and CTP, 

 mono-, di- and triphosphates of cytidine, respectively; GMP, GTP, mono- and 

 triphosphates of guanosine, respectively ; ATP, adenosine triphosphate ; TTP, 

 th\Tnidine triphosphate ; deoxycompounds are denoted by the prefix d-. 



