FIG. 1.

Diagram of bar-coded antibiotic resistance cassettes. Kanamycin resistance cassettes flanked by two unique 20-mer DNA bar code sequences (UP and DN) were generated by a two-step PCR process for each deleted gene. The bar-coded kanamycin resistance cassettes were incorporated at loci coding for sRNAs and small proteins by homologous recombination. For the analysis of the large-scale competition experiments, bar codes upstream and downstream of every kanamycin resistance cassette were amplified by means of common primer sequences (indicated by small black arrows) encoded within the regions bordering the UP and DN bar codes. The amplified bar codes were then hybridized to a DNA microarray to score each bar-coded deletion mutant within the population.