26 



MArRICE J. BESSMAN 



As shown in T:il)le VI, DNA treated with l)Nas;e loses its capacity to 

 support synthesis. Other polymers which have been tested (Bessnian 

 et al., 1957) and found ineffective as primers arc apurinic acid, turnii) 

 yellow mosaic virus RNA, and a polythymidylic acid polymer (kindly 

 provided by H. Gobind Khorana). 



The important feature of the priming DNA seems to lie in its primary 

 structure since many treatments designed to destroy the hydrogen bond- 

 ing between the specific base pairs of double helices (Watson and Crick, 

 1953a) not only do not destroy priming ability but in some instances 

 actually enhance it. In Table X, for example, native DNA is compared 



TABLE X 

 Enzymatic Synthesis of Viscous DNA from Non-Viscous Primers" 



" From Lehman (1959). 



to heat-denatured DNA and "natural" single-stranded DNA (Sins- 

 heimer, 1959). It can be seen that the "denatured" or single-stranded 

 DNA primes synthesis at twice the rate and to the same extent as the 

 natural DNA. Furthermore, the products of the reaction are in all cases 

 viscous even though the heated, and single-stranded DNA are non- 

 viscous preparations. 



An interesting observation (Lehman, 1959) is the improvement of 

 calf thymus DNA as a primer by treating it with minute amounts of 

 pancreatic DNase: 



MgDNA 

 Mg DNase 



= 2 X lO'^ 



DNA treated in this manner primes syntheses at 2 to 3 times the rate of 

 untreated primer. It is possible that this treatment provides more free 

 3'-hydroxyl groups for condensation with the deoxynucleoside triphos- 

 phates. Alternatively, the pretreatment could provide weak points 



