Repressor and rex product of coliphage lambda: Lack of collaboration and joint controls

The Time Required for cro Gene Product to Establish Dominance in Coliphage Lambda Lysogens

“…1, it can be seen that the control grown at 30 °C without exposure to 41 °C maintained a steady level of rex gene activity throughout the 14 h of culture. On the other hand, the control grown at 41 °C continuously for 14 h lost the rex gene activity (becoming rex-) after 3 to 5 h of culture at 41 °C, as observed previously (Mark & Szybalski, 1973). The cultures with short exposure to 41 °C followed by a long period of culture at 30 °C appeared to have a fraction of the cells beconing rex-.…”

“…Now the lysogen has imm-and rex-phenotype. This state is known as the ira-phase Mark & Szybalski, 1973). Because of this correlation the rex-phenotype can be used as an indicator for the im-phase.…”

“…+) were used as controls and 594(3-N7cI857Odef3) was the test lysogen. This lysogen was isolated by Dr H. Inokuchi, and can grow at 41 °C without being killed (Mark & Szybalski, 1973). The stock culture was purified, grown up at 30 °C and stored in the cold to 0022-1317/82/0000-4723 $02.00©1982 SGM make sure that all lysogenic cells had the rex + phenotype before the experiments took place.…”

“…The last fraction was retained at 41 °C for the entire 14 h of culture to serve as a reference for the im-phase. Although the synthesis of the rex gene product and the lambda repressor can be terminated by the action of the cro gene product, the removal of the existing rex gene product and the lambda repressor in the cell require many generations of growth to dilute them out (Mark & Szybalski, 1973). This was done by maintaining the cultures for 14 h in the exponential phase of growth at a concentration of 2 x 10 s to 3 x 10 s cells/ml by regular dilution with prewarmed tryptone broth supplemented with tryptophan.…”

The Rex system of bacteriophage lambda: tolerance and altruistic cell death.

“…We expect that exclusion will decay most rapidly in an induced lysogen {cro'^ O"^) that is capable of only LIT transcription. Unfortunately, the published data for cro'^ O"^ lysogens (Mark and Szybalski 1973;Toothman and Herskowitz 1980a) are inconclusive.…”