Figure 5. oriC4 is essential for chromosome replication in the absence of the other three origins.

(a) Cells of the DF50 and DF50ΔoriC1ΔoriC2ΔoriC3 (DF50Δ123) strains and of the corresponding trpA knockout mutant strains, named DFA50 and DFA50ΔoriC1ΔoriC2ΔoriC3 (DFA50Δ123), respectively, were streaked onto AS-168SY plates supplemented with uracil and with or without tryptophan. (b) For the positive selection of trpA-marked knockouts of oriC4 in DFA50 and DFA50ΔoriC1ΔoriC2ΔoriC3, the corresponding propagated culture of one pop-in colony in the AS-168 broth was plated on AS-168SY plates supplemented with uracil and 5-FOA and without tryptophan. *The cell density of the corresponding culture of DFA50ΔoriC1ΔoriC2ΔoriC3 for plating was 10 times that of DFA50.