A test of the directed mutation hypothesis in Escherichia coli MCS2 using replica plating.

Excision of phage Mu from Escherichia coli MCS2 was originally put forth as a clear example of directed mutation. This claim was considerably weakened, however, by subsequent evidence that Mu excision occurs during starvation regardless of fitness consequences. Here, I use the classical replica-plating technique to examine Mu excision during starvation of MCS2. The results support the conclusion that Mu excision is not directed but is, instead, nonspecifically induced by starvation.