S. SPIEGELMAN AND A. M. CAMPBELL 



that X-ray dosages far exceeding those expected to stop the for- 

 mation of DNA completely permit normal enzyme formation in 

 yeast. Similar dissociations have been achieved with other 

 systems and by different means (30,58). 



Kelner's (43) studies on photoreactivation of E. coli fol- 

 lowing exposure to ultraviolet have provided an elegant method 

 for a virtually complete separation of RNA and protein forma- 

 tion from net DNA synthesis. Halvorson and Jackson (31) 

 employing yeast have recently repeated and confirmed these 

 results. The results obtained suggest again that protein and 

 RNA continue to be synthesized subsequent to UV doses which 

 completely inhibit the DNA formation. 



Cohen and Earner (16) have reported the ability of a 

 thymine-less mutant of E. coli which can synthesize xylose isom- 

 erase in the absence of an added supply of thymine. This im- 

 portant finding was confirmed in our laboratory (85) using the 

 same mutant and examining beta-galactosidase-forming capac- 

 ity. It was found that cells of this strain synthesized consider- 

 able amounts of enzyme when suspended in a synthetic medium 

 lacking thymine. This behavior is in striking contrast to tliat 

 observed with mutants possessing other metabolic deficiencies. 

 Thus, in our own experience and in that of others (56,58,85), 

 adenine-less, uracil-less, or amino-acid-deficient mutants form 

 little or no enzyme in the absence of the required metabolite. 



An interesting apparent exception to the information cited 

 is that of Allfrey's (2) observation with isolated nuclei. He found 

 that treatment with DNase suppressed the ability of his prepara- 

 tions to incorporate labeled amino acids, whereas RNase had 

 little or no effect. The situation observed here may, however, be 

 a reflection of the low nuclear RNA content. If, as seems likely, 

 RNA is derived from DNA, destruction of the latter would elim- 

 inate protein synthesis in such systems. 



The data cited above demonstrate that drastic interference 

 with DNA synthesis is often not accompanied by very striking 

 effects on the formation of protein. Whereas such findings can- 

 not eliminate DNA as an active component of the EFS, they 



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