Fig. 6

Nucleotide distribution at splice sites (ss) of internal introns. Five nucleotides up- and downstream of each splice site are shown in weblogos. The height of the nucleotide letters indicates the frequency of each nucleic acid at the respective position. Sequence logos at the left depict splice sites of hemocyanins of Tectipleura; those at the right of Lepetellida, Octopodoidea and Nautilus pompilius (taken together as non-Tectipleura hemocyanins). Internal introns are further distinguished in introns at multiple (top, black dot, cf. Fig. 4) and introns at unique splice site positions (bottom, open dot, cf. Fig. 4). Multiple splice site positions are defined as positions along the cDNA where at least one different intron is located (cf. Fig. 4). This can be located in a different FU of the same gene structure type or in any FU of a different gene structure type. At unique splice site positions, no introns of other FUs/hemocyanins are located at the identical position with respect to the coding sequence (cf. Fig. 4). The intronic splice site GT-AG is highly conserved throughout all hemocyanins. Additionally, weblogos display the existence of the (exonic) proto-splice site AG|G. For better comparison of the frequency of AG|G in the four different weblogos, black double arrows of the same height are given. While all proto-splice site nucleotides of multiple splice site positions of Tectipleura and non-Tectipleura (upper ones) are higher than those reference arrows, some of the unique splice site positions are much smaller