284 J. D. SMITH 



At pH 9.2 in borate buffer the bases, the ribonucleosides, and the nucleo- 

 tides may be separated into three groups in that order. ^"^ 



Addendum 



Microtechnique of Electrophoresis 



The electrophoretic techniques hitherto described are suitable for the 

 separation and analysis of the nucleotides or bases from 100 Mg- or more of 

 nucleic acid. Edstrom*" has developed a method which permits the analysis 

 of 100-1000 pg. of ribonucleic acid (1 pg. = 10~^- g.), which is of the same 

 order as the amount contained in single nerve cells. 



The supporting medium is a piece of copper-silk (cellulose) previously 

 treated with alkali to swell the fibers. The fiber is soaked in a highly viscous 

 citrate buffer pH 3.6, containing glucose and glycerol, and stretched on a 

 quartz slide between dabs of paste moistened with the buffer. During the 

 electrophoresis the fiber is immersed in liquid paraffin. The substances 

 to be separated are placed on the fiber with a micropipet and a potential 

 applied through platinum electrodes between the dabs of paste. With a 

 voltage gradient of 12 v./mm. the adenine, guanine, and cytidyhc and 

 uridylic acids from a hydrolysate of PNA in A^ HCl are separated in 2 hr. 

 over a distance of 1 mm. The fiber is photographed together with a light 

 calibration system in monochromatic light of 257 mn and 275 m^, respec- 

 tively, and the densities of the calibration system and parts of the fiber are 

 measured photometrically on a photographic strip. 



Detection of Terminal 5' -Phosphate Groups in Ribonucleic Acids 



Markham, Matthews, and Smith^^ have shown that the ribonucleic acids 

 of tobacco mosaic virus and potato virus X contain a type of chain which is 

 terminated at one end by a nucleoside residue bearing a singly esterified 

 phosphate group on the 5'-position and at the other end by a nucleoside 

 residue with no singly esterified phosphate group. On alkaline hydrolysis 

 this type of chain gives in addition to mononucleotides, nucleoside-2' , 5'- 

 and nucleoside-3',5'-phosphates from the terminal residues bearing the 

 phosphate groups, and nucleosides from the other end of the chain. These 

 can be separated by paper electrophoresis at pH 7.4 when the nucleosides, 

 which are uncharged, remain at the starting point while the nucleoside 

 diphosphates which carry four negative charges move towards the anode 

 ahead of the nucleoside monophosphates. 



30 J. E. Edstrom, Nature 172, 809 (1953). 



" R. Markham, R. E. F. Matthews, and J. D. Smith, Nature 173, 537 (1954), 



