Co-localisation of spanion clusters and experimentally detected tiRNAs. The distribution of the distances between the upstream end of a spanioncluster and the downstream end of the closest reported tiRNA hit in upstream position relative to the spanioncluster . The real dataset is marked by squares; the reference set (continuous line) was generated as in the case of the RNA polymerase II dataset (see above). The typical size of the tiRNAs and the spanionclusters is directly comparable: 20 - 25 bases. The peak at -20 indicates that typically the 5' ends of the two kinds of segments are only a couple of bases apart.