Densities of high GC-content PPTs relative to human hot spot locations. Sliding window plots of the densities of PPTs of at least 12 bp, with GC-contents above the mean for PPTs over the regions we investigated, relative to hot spot locations in A): a 292 kb region of the human MHC Class II region in which 7 hot spots are known and B): a 206 kb region of human chromosome 1 in which 8 hot spots are known. Vertical dotted lines represent hot spot mid point locations. Sliding windows were 10 kb wide and moved in steps of 100 bp. Locations of genes in the regions are shown below the plots with arrows indicating direction of transcription.