A deletion analysis of prophage lambda and adjacent genetic regions.

The attachment site of the X prophage on the chromosome of Escherichia coli K-12 is between the gal operon and the bio region.' (Symbols used for genes of E. coli are given in Taylor and Trotter.6) The order of prophage markers is a cyclic permutation of that in the vegetative phage.2-5 Recently, linkage to the gal-bio region has been shown for several other markers: aroG, aroA, chlA, and uvrB. Chlorate is toxic to E. coli K-12 under anaerobiosis. The toxic compound is probably not chlorate perse but rather chlorite or some other reduction product of chlorate that arises through the agency of an enzymatic system capable of reducing nitrate as well as chlorate. Mutants that are resistant to chlorate and are also defective in nitrate reductase activity can be isolated.7 The mutants were classified in three groups-chlA, chlB, and chlC which are linked to gal, intl and try, respectively.8 The chiA locus was provisionally mapped between gal and bio by crossing chl-s and chl-r strains marked in the gal and bio regions.7 The present report describes more definitive mapping of the chlA locus, as well as other markers in this region, including a new locus for chlorate resistance (chlD). T-Nlapping of these loci included the use of bacterial deletion mutants, some of which penetrate the X prophage. Some properties of the prophage deletions that are relevant to the general biology of phage X are described.