Distribution of A- and T-runs at SLS termini. Intergenic SLSs from the indicated genomes with a dG < -10 KCal/mole and a loop length < 30 nt, located 20 bp or less from the stop codons of CDSs (large grey bars) were screened for the presence of either A- or T-tetramers or both tetramer types at the 5' and 3' borders. Border is defined here as the 10 nt long region including, in each SLS, the first 5 nt of the stem and the 5 nt located immediately outside of the stem, either at the 5' or the 3' side (see inset in panel A). A) For each analyzed species, the four bars respectively indicate the number of SLSs containing 5'T-, 5'A-,3'T-and 3A'-runs of at least four identical residues. The black portions of the bars indicate the contemporary presence of both 5'As and 3'Ts. The height of the light grey regions in the background represents the total number of SLSs in the analyzed pools. B) The fraction of SLSs carrying 3'T-runs (grey bars) or both 5'A- and 3'T-runs (black bars) in the analyzed genomes is shown.