Sequencing the ends of the 5 kb band revealed the known IS5 element b1331 to the right of ynaI on one side and a new IS5 element inserted to the left of ogt (b1335) on the other. This result seems to indicate that the strain of W3110 deposited with CGSC has two copies of IS5 on either side of ynaJ, uspE and fnr that undergo recombination with each other at high frequency leading to the deletion of the intervening genes. The remaining 22 clusters of ROI probes were PCR amplified and Sanger sequenced to see if they indicated additional mutations not present in the W3110 genome sequence. Indeed, seven IS-element insertions were discovered, while the other 15 clusters showed no mutations. We note that all but one of the false positive ROIs were single-probe clusters and that all of them contained inverted repeats of between 6 and 13 nt. These repeats may lead to hairpin structures and poor hybridization properties of those probes [15] . In total, 10 mutations (2 SNPs, 7 IS-insertions and 1 deletion) accumulated in strain W3110 in the time period between when Kohara et al. generated the lambda library and when we obtained it from CGSC. The history and handling of the strain before Ishihama deposited it with CGSC in 1990 is not known by the authors of this study, though we speculate that it may have been stored as a stab at room temperature.