32 MOLECULES, VIRUSES, AND BACTERIA 



thymidylate kinase is blocked by chloramphenicol, suggesting the syn- 

 thesis of protein (Bessman, 1959). As in the case of the thymidylate 

 synthetase described above, it may be asked whether the increase in 

 these kinases represents more of the old enzymes or of new types of 

 polypeptides having similar active sites. Bessman and van Bibber 

 (1959) have reported that the dGMP kinase formed after infection no 

 longer has the requirement for K+ that is characteristic of the kinase 

 formed before infection. 



Given the dHTP and the other normal triphosphates, several 

 groups (Kornberg et al., 1959; Koemer et al., 1959) have studied the 

 polymerase present after infection and its activity in the synthesis of a 

 DNA-containing HMC. About a ten-fold increment has been seen in 

 the DNA polymerase, and the purified enzyme of both uninfected and 

 infected cells appears to be able to handle dCTP as well as dHTP. In 

 these tests heated DNA derived from T2 or calf thymus can be used 

 interchangeably. 



Koemer et al. (1959) have prepared a monoglucosyl dHTP and 

 have observed that this does not participate in the reaction with DNA 

 polymerase. On the other hand, DNA-containing HMC, generated 

 from dHTP and DNA polymerase, can be monoglucosylated in part by 

 UDPG in the presence of a new enzyme formed in bacteria infected by 

 T2 ( Kornberg et al., 1959 ) . Extending this important observation ( A. 

 Kornberg, personal communication ) , it appears that two separable en- 

 zymes are formed in T4-infected cells— one which adds on a small 

 amount of glucose to T2 DNA and a second which converts T2 DNA 

 to a form in which all HMC is completely monoglucosylated. Two 

 separable enzymes are also present in T6 infected cells— one like that 

 in T2-infected cells and a second which does not monoglucosylate but 

 adds a second glucose to T2 DNA and T4 DNA. 



With the apparent synthesis of 13 enzymes in the first minutes 

 after infection, we are finally in a position to account, in outline at 

 least, for the stimulated DNA synthesis observed so many years ago 

 (Cohen, 1947). These phage-infected bacteria are evidently a source 

 par excellence for the study not only of th© individual enzymes, since 

 they are present in extraordinarily high concentration, but also of the 

 specific control and kinetics of protein synthesis by specific DNA. 

 However, in addition there are many other problems which remain in 

 this system: e.g., when are the other viral proteins produced and how 

 are these syntheses related to the production of viral DNA? 



Of the viral proteins, the internal "gut" protein of Levine et al. 

 (1958) is unique in appearing with the enzymes of DNA synthesis. 

 Using an immuno-chemical method, this specific protein is detectable 

 two to three minutes after infection ( Murakami et al., 1959 ) . As with 

 the hydroxymethylase, infection with ultraviolet-irradiated phage in- 



