Top. Scatter plot of the number of overlapping sequences versus the total number of overlapping bases for the 58 investigated genomes. The line is a best linear fit and gives a typical overlap length of 26 bp. The analysis is performed by considering only overlapping genes which are both annotated in the COG database. Bottom. Cumulative density function of the length of overlapping sequences in the whole dataset (14, 958 overlaps). The red dashed line is the best fit of the distribution with an exponential function exp(-ax). The blue line is the cumulative density function only for conserved ORs (see text). The green dashed line is a best fit and the estimated exponent is 2.5. The plot is log-log. The inset shows the probability density function of overlap length in the range of short ORs.