Figure 4

Plot of A+C and G+T composition along mtDNAs of Nautilus macromphalus and Katharina tunicata using a sliding window of 100 nucleotides. In each case, the nucleotide composition is being shown for the strand reported, i.e. the one that is the sense strand for cox1. Numbering of nucleotides begins at the arbitrarily chosen cox1 (as in Additional file 4 for N. macromphalus). The scaled gene maps are also presented. tRNA genes are pictured but not labeled. Underlining and light shading indicates opposite, i.e. right-to-left transcriptional orientation. Numerals label each non-coding region larger than 20 nts, which are then projected onto the plot by gray highlighting. Several of these correspond to positions where there is a shift in nucleotide bias. Asterisks beside two of the numerals for K. tunicata indicate some ambiguity where these may instead be supernumerary tRNA genes [28]. Red bars show the major transposition between the two genomes (see Fig. 2).