Effects of 5-Bromodesoxyuridine upon Gene Recombination in Escherichia Coli K-12.

ENETIC analyses of crosses of E. coli IS-I2 Hfr x Fhave demonstrated that Gfactors possessed by the donor parent (Hfr) are transferred in a characteristic, oriented, and progressive manner to the recipient (F-) parent ( WOLLMAN, JACOB, and HAYES 1956), and that recombinants segregate only from the Fparent ( LEDERBERG 1956). The transfer of radiophosphorous-containing material (probably DNA) has been correlated with the transfer of genetic factors by GAREN and SKAAR (1958), while experiments of JACOB and WOLLMAN (1954) and PARDEE, JACOB and WOLLMAN (1958) indicate that little, if any, cytoplasmic transfer occurs during conjugation. It is for these reasons that E. coli K-12 has proven to be a particularly suitable system in which to test the effects of agents, such as ultraviolet irradiation or radiophosphorous disintegration, upon genetic recombination (JACOB and WOLLMAN 1958). If the donor of genetic material is treated with these agents and permitted to conjugate with appropriate Fcells, nonspecific physiological effects can be resolved from those which affect the genetic material. By subjecting donor bacteria to low doses of ultraviolet irradiation, significant increases in the frequency of gene recombination have been obtained by JACOB and WOLLMAN (1958). These authors assert that the mechanism best explaining their data is one based upon the partial replica hypothesis (LEVINTHAL 1954). According to this hypothesis, a new recombinant segment of genetic material arises by alternately copying from one, then the other, of two paired homologous strands. They suggest that lesions are formed upon ultraviolet treated genetic material, which represent sites along its length and interfere with normal replication by causing the newly formed strand to switch back to the nonirradiated segment for completion of replication. Since the mode of action of ultraviolet irradiation is incompletely understood, these experiments do not test directly the partial replica hypothesis. Other agents whose action upon genetic material can be more clearly inferred are desirable to test this hypothesis. The nucleic acid base analogue 5-bromouracil is specifically incorporated into