A λ ZAP expression library of E.coli genomic DNA has been constructed. Screening the library with the Era protein probe labeled by digoxigenin, a plaque specially bound with Era has been isolated from 4×10⁴ plaques. It is confirmed that an Era-binding protein gene exists in E.coli genomic DNA. Compared with the data in GenBank, the 5′ end 800 bp of inserted DNA is located in the section 267 of E.coli genomic DNA.