The article describes a sensitive and general technique for cloning genes using antibodies as probes and isolating unknown proteins encoded by cloned DNA. The method involves using the λgt11 expression vector, which allows the insertion of foreign DNA into the β-galactosidase structural gene lacZ and promotes the synthesis of hybrid proteins. The technique is based on high-frequency lysogeny in Escherichia coli h14 mutant cells, which enables efficient screening of antigen-producing clones in λgt11 recombinant cDNA libraries. The vector is designed to facilitate the isolation of proteins specified by previously cloned gene sequences, with hybrid proteins accumulating in strains defective in protein degradation (lon mutants). Antibodies produced against the portion of the hybrid protein encoded by foreign DNA can be used to isolate the native polypeptide from eukaryotic cells. The authors detail the construction of the λgt11 vector, its properties, and the methods for preparing antibodies and screening λgt11 recombinant DNA libraries with antibody probes. They also demonstrate the successful detection of antigen produced by induced lysogens containing λgt11 recombinant phage, even at high cell densities. The study highlights the potential of this method for isolating gene sequences and unknown native proteins.The article describes a sensitive and general technique for cloning genes using antibodies as probes and isolating unknown proteins encoded by cloned DNA. The method involves using the λgt11 expression vector, which allows the insertion of foreign DNA into the β-galactosidase structural gene lacZ and promotes the synthesis of hybrid proteins. The technique is based on high-frequency lysogeny in Escherichia coli h14 mutant cells, which enables efficient screening of antigen-producing clones in λgt11 recombinant cDNA libraries. The vector is designed to facilitate the isolation of proteins specified by previously cloned gene sequences, with hybrid proteins accumulating in strains defective in protein degradation (lon mutants). Antibodies produced against the portion of the hybrid protein encoded by foreign DNA can be used to isolate the native polypeptide from eukaryotic cells. The authors detail the construction of the λgt11 vector, its properties, and the methods for preparing antibodies and screening λgt11 recombinant DNA libraries with antibody probes. They also demonstrate the successful detection of antigen produced by induced lysogens containing λgt11 recombinant phage, even at high cell densities. The study highlights the potential of this method for isolating gene sequences and unknown native proteins.