The landscape of genomic DNA in the region of human and mouse Tlr4 genes. Approximately 19 kb of sequence is shown from each species. Exons are numbered 1 to 3. In the human gene model, an added exon (f) is also portrayed, as found in the alternative sequence of Rock et al. , in which early truncation of the protein is predicted. The grayscale image was generated using X-GRAIL, version 1.3c, and depicts GC content as well as repetitive elements (both complex and simple) identified by RepeatMasker (which appear as unbroken stretches of white). GC-rich areas appear darker than AT-rich areas. Grail exons are shown in green (highest quality) and blue (intermediate quality) above each grayscale image. Restriction sites indicate enzymes that cut at single sites within the interval.