Genetical Research

Research Article

The dominance of exrB over exrB+ in heterodiploids of Escherichia coli*

Joseph Greenberga1, John Doncha1 and Leonard Berendsa1

a1 Palo Alto Medical Research Foundation, Palo Alto, California


To test whether exrB, a mutation in Escherichia coli B making this strain sensitive to ultraviolet radiation and unable to divide normally, is dominant to exrB+, merodiploids were constructed by crossing Hfr exrB metA+ his × F malB met A thr proA recA. metA+recombinants were fertile (F′) and sensitive to UV. One of these, F′ exrB proA, was crossed with an F metA malB thr, selecting for metA+ proA+. All such progeny acquiring malB+ were UV-sensitive, fertile and segregated met mal UV-resistant progeny. They were, therefore, meriodiploids, F′ exrB/exrB+. exrB is dominant to exrB+, in which respect it resembles exrA (lex).

(Received July 29 1974)


* This investigation was supported by Public Health Service Grant CA 05687–13 from the National Cancer Institute, the Santa Clara County United Fund and the Harvey Bassett Clarke Foundation.