The Keio collection is a comprehensive set of precisely defined, single-gene deletions of all nonessential genes in Escherichia coli K-12. This collection was created using a one-step method involving PCR products with a kanamycin resistance cassette flanked by FLP recognition sites. The method allows for in-frame deletions upon excision of the resistance cassette. Of 4288 targeted genes, mutants were obtained for 3985, with two independent mutants saved for each gene. The collection provides a valuable resource for systematic analysis of gene functions and gene regulatory networks, as well as for genome-wide testing of mutational effects in a common strain background. However, 303 genes, including 37 of unknown function, could not be disrupted, suggesting they may be essential. The collection is distributed via GenoBase and includes a large number of mutants, which have been used in various studies to analyze gene function and metabolism. The Keio collection is a key resource for functional genomics and systems biology, offering a systematic approach to understanding gene function and cellular processes in E. coli. The collection has been used in numerous studies to investigate gene function, metabolism, and other biological processes. The collection is also useful for studying the conservation of essential genes in other organisms. The collection has been widely distributed and is an important resource for the scientific community. The collection includes mutants for 3985 genes, with two independent mutants for each gene. The collection has been used in various studies to analyze gene function and metabolism. The collection is a key resource for functional genomics and systems biology, offering a systematic approach to understanding gene function and cellular processes in E. coli. The collection has been used in numerous studies to investigate gene function, metabolism, and other biological processes. The collection is also useful for studying the conservation of essential genes in other organisms. The collection has been widely distributed and is an important resource for the scientific community.The Keio collection is a comprehensive set of precisely defined, single-gene deletions of all nonessential genes in Escherichia coli K-12. This collection was created using a one-step method involving PCR products with a kanamycin resistance cassette flanked by FLP recognition sites. The method allows for in-frame deletions upon excision of the resistance cassette. Of 4288 targeted genes, mutants were obtained for 3985, with two independent mutants saved for each gene. The collection provides a valuable resource for systematic analysis of gene functions and gene regulatory networks, as well as for genome-wide testing of mutational effects in a common strain background. However, 303 genes, including 37 of unknown function, could not be disrupted, suggesting they may be essential. The collection is distributed via GenoBase and includes a large number of mutants, which have been used in various studies to analyze gene function and metabolism. The Keio collection is a key resource for functional genomics and systems biology, offering a systematic approach to understanding gene function and cellular processes in E. coli. The collection has been used in numerous studies to investigate gene function, metabolism, and other biological processes. The collection is also useful for studying the conservation of essential genes in other organisms. The collection has been widely distributed and is an important resource for the scientific community. The collection includes mutants for 3985 genes, with two independent mutants for each gene. The collection has been used in various studies to analyze gene function and metabolism. The collection is a key resource for functional genomics and systems biology, offering a systematic approach to understanding gene function and cellular processes in E. coli. The collection has been used in numerous studies to investigate gene function, metabolism, and other biological processes. The collection is also useful for studying the conservation of essential genes in other organisms. The collection has been widely distributed and is an important resource for the scientific community.