Abstract
Four genes of Escherichia coli whose products are needed to reduce biotin- d -sulfoxide to biotin have been mapped: bisA next to chlA, bisB next to chlE, bisC linked to xyl , and bisD next to chlG . A defective λ transducing phage, λ dbis5 , which carries all the bacterial genes between the λ attachment site and chlE , was isolated and shown to have lost the phage genes from int through Q .