The rIIB gene of bacteriophage T4 in genetic recombination

The effect of the rIIB gene on genetic recombination in bacteriophage T4 wa s studied. Relationships between recombination frequency and the physical d istance were determined in three series of isomarker two-factor crosses bet ween rII mutants. In the first series of intergenic crosses (rIIa x rIIb), the rII gene function was restored owing to complementation. In the second series of crosses, identical to the first one, the rIIB gene function was s uppressed, because the rIIa parent carried an additional amberlike mutation in the rIIB gene. The recombinants were scored by plating lysates on the a mber-suppressor Escherichia coli strain, on which an amberlike mutation was not expressed phenotypically. In the third series, all crosses were intrag enic (rIIb x rIIb). In two series of crosses in the absence of the rIIB fun ction, the relationships between recombination frequency and the physical d istance were identical, whereas enhanced recombination frequencies were obs erved in the rIIB(+) background. The magnitude of the rIIB-related effect d epended on distance, reaching the maximum in the region located 100 to 200 bp from the beginning of the rIIB gene. The possible role of the rIIB prote in in genetic recombination is discussed.