Bg. Hall, THE ROLE OF SINGLE-MUTANT INTERMEDIATES IN THE GENERATION OF TRPAB DOUBLE REVERTANTS DURING PROLONGED SELECTION, Journal of bacteriology, 175(20), 1993, pp. 6411-6414
Selection-induced mutations are nonrandom mutations that occur as spec
ific, direct responses to environmental challenges and that occur more
often when they are selectively advantageous than when they are selec
tively neutral. One of the most puzzling examples of selection-induced
mutations involved the simultaneous reversions of two mutations, one
in trpA and the other in trpB, at rates that were several orders of ma
gnitude greater than would have been predicted if the two mutations ha
d occurred as independent events (B. G. Hall, Proc. Natl. Acad. Sci. U
SA 88:5882-5886, 1991). Here I examine the possibility that the double
mutations might be accounted for by sequential mutations with interve
ning growth.