[lambda]imm[lambda][middle dot]434: A phage with a hybrid immunity region

Abstract

The genomes of coliphages [lambda] and [lambda]imm434 are identical with the exception of the immunity region, which codes for the respective repressors and corresponding operators. Although previous genetic studies failed to detect any recombinations that might have occurred within the immunity regions of these two phages, electron-micrographic heteroduplex mapping demonstrated a short interval of homology between [lambda] and [lambda]imm434 DNA located in this otherwise heterologous region. We report the isolation of a recombinant which resulted from a cross-over event between [lambda] and [lambda]imm434 within the immunity region. This phage, denoted [lambda]imm[lambda][middle dot]434, carries the leftward promoter-operator as well as gene rex of [lambda] and the rightward promoter-operator as well as gene tof (cro) of phage 434. Since the recombination occurred within the cI gene, phage [lambda]imm[lambda][middle dot]434 must carry a hybrid repressor gene.