CONTROL BY REPRESSION 45 



which characteristically are heterogeneous and in a highly dynamic 

 state. Other advances have come from recent studies with extracted 

 ribosomal systems, which made it possible to obtain in vitro syn- 

 thesis of induced (Kameyama and Novelli, 1960) and constitutive 

 (Nisman and Fukuhara, 1960) /S-galactosidase. Rogers and Novelli 

 ( 1960) have adduced evidence for the in vitro formation of ornithine 

 transcarbamylase. Kameyama and Novelli (1960) demonstrated 

 an inducer-dependent synthesis of ^S-galactosidase that is inhibited 

 bv chloramphenicol, ribonuclease, or deoxyribonuclease. These re- 

 sults indicate, amone; other things, an involvement of ribonucleic 

 and deoxvribonucleic acids in the synthesis of this enzyme. The 

 intimate connection that seems to exist between ^-galactosidase for- 

 mation and deoxyribonucleic acid has recently been underscored by 

 several different lines of evidence. Nisman and Fukuhara ( 1960 ) 

 noted a stimulation of the in vitro formation of constitutive )S-galac- 

 tosidase attributable to deoxyribonucleic acid. A continuing role 

 of deoxyribonucleic acid in yS-galactosidase formation is also indi- 

 cated by the fact that irradiation of bacteria with ultraviolet light 

 (Rushizkv et al., 1960; Novelli, 1960) or infection of the bacteria 

 with T2 phage (Novelli, 1960) readily stops the formation of this 

 enzyme. A similar indication lias come from P^- decay experiments 

 in zygotes (Riley et al., 1960). After "thymine saturation," i.e., 

 when deoxvribonucleic acid presumably exists as fully paired strands 

 (Maal0e and Hannawalt, 1960), both induced ^-galactosidase for- 

 mation ( Fig. 2-6 ) and synthesis of deoxyribonucleic acid show a lag 

 and then proceed hand in hand ( Roberts, 1960 ) . These various re- 

 sults do not, however, force the conclusion that the induction of the 

 enzvme requires concomitant deoxyribonucleic acid synthesis. Rob- 

 erts (1960) suggested that the critical factor may be the availability 

 of deoxyribonucleic acid in the proper state. In the thymine-satu- 

 rated condition, deoxyribonucleic acid, in view of the lag, could be 

 inactive for this induction, but other interpretations of these results 

 have not been ruled out. Significantlv, cells that are non-inducible 

 due to thymine starvation seem to be able to svnthesize the enzyme 

 at a level of the order of magnitude of the usual non-induced ( basal ) 

 level (Roberts, 1960). 



The ornithine transcarbamylase system is indicated to stand in 

 contrast to the ^-galactosidase system with respect to dependence 

 on deoxyribonucleic acid: the derepressed synthesis of the trans- 

 carbamvlase is not immediately affected by phage infection and is 



