Isolation and characterization of plaque-forming lambdadnaZ+ transducing bacteriophages

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Abstract
The Escherichia coli dnaZ gene, a DNA polymerization gene, is located 1.2 min counterclockwise from purE, at .apprx. 10.5 min on the E. coli map. From a lysogen with .lambda.cI857 integrated at a secondary attachment site near purE, transducing phages (.lambda.dnaZ+) that transduced a dnaZts (.lambda.+) recipient to temperature insensitivity (TS+) were discovered. Three different plaque-forming transducing phages were isolated from 7 primary heterogenotes. Genetic tests and heteroduplex mapping were used to determine the length and position of E. coli DNA within the .lambda. DNA. Complementation tests demonstrated that the deletions in all 3 strains removed att P and the int gene, i.e., DNA from both prophage ends. Heteroduplex mapping confirmed this result by demonstrating that all 3 strains had deletions of .lambda. DNA that covered the b2 to red region, thereby removing both prophage ends. Specifically, the deletions removed .lambda. DNA between the points 39.3-66.5% of .lambda. length (measured in percent length from the left end of .lambda. phage DNA) in all 3 strains. The 3 strains are distinct because they had differing lengths of host DNA insertions. These phages must have been formed by an anomalous procedure, because standard .lambda. transducing phages are deleted for 1 prophage end only. In .lambda.gal and .lambda.bio strains the deletions of .lambda. DNA begin at the union of prophage ends (i.e., position 57.3% of .lambda. length) and extend leftward or rightward, respectively. Models for formation of the .lambda.dnaZ+ phages are discussed.