Percentage of antisense transcripts per genome. Experimentally determined number of antisense transcripts in Archaea (Koide et al. 2009; Wurtzel et al. 2010) and Bacteria (Cho et al. 2009; Guell et al. 2009; Liu et al. 2009; Rasmussen et al. 2009; this study) correlated with genome size (open circles). Percentage of antisense transcripts in a genome-reduced E. coli strain (Posfai et al. 2006) is shown as a gray circle. Number of antisense transcripts per genes detected (i.e., experimental coverage) was extrapolated to whole genomes.