Gene organization of seven <i>rrn</i> operons in the <i>E</i>. <i>coli</i> K-12 genome.

<p>Seven rRNA operons exist in more than 2,000 <i>E</i>. <i>coli</i> strains so far sequenced [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144697#pone.0144697.ref039" target="_blank">39</a>]. Two K-12 strains, MG1655 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144697#pone.0144697.ref007" target="_blank">7</a>] and W3110 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144697#pone.0144697.ref008" target="_blank">8</a>], are widely used as the model <i>E</i>. <i>coli</i> strains. Strain W3110 carries an inversion between <i>rrnD</i> and <i>rrnE</i> operons [A], but the direction of transcription for all seven <i>rrn</i> operons are the same with that of DNA replication in both strains. The order of rRNA organization in seven <i>rrn</i> operons are the same, but each <i>rrn</i> operon contains one to three different tRNA genes [B]. Details are described in text.