One novel cluster of ROI probes was very large, indicating the possible deletion of three genes, ynaJ, uspE, and fnr (b1332-1334). Such a deletion is not present in the genome sequence of W3110. PCR amplification using primers located in adjacent genes confirmed the deletion; a 3.8 kb PCR product was obtained from MG1655 while a 1.4 kb product was obtained from W3110. Deletions of fnr have been noted previously in strains of MG1655 obtained from the CGSC [16] . To determine if the deletion occurred before or after the strain was deposited at CGSC, a culture was obtained from the original lyophil made when stock # 7167 was deposited in 1990 by Akira Ishihama. PCR amplification with the same primers showed two products, one at 1.4 kb and another at 5 kb.