Fig. 3

Sequence features of the IG1-intron at the nucleotide and protein levels. a, c MUSCLE alignment of 50 nucleotides that span the AGGT exon–intron (a), or the intron–exon (c), boundaries of the IG1-intron. Data are from 23 species representative of the metazoan phyla that encode DG. b, d Multiple sequence alignments prepared in MUSCLE 3.8 of 15 aa long regions from the IG1 domain that flank the exon–intron insertion site (b), or the intron–exon site (d) in the same species. The region shown in b includes a.a. 81–95 of human DG; the region shown in d includes a.a. 96–110 of human DG. e The secondary structural elements of the IG1 domain that encompass the intron insertion site (⁹⁵KV⁹⁶ in human DG, underlined) [11] demonstrate that the intronic sequence is not in register with the structural organization of the domain. f MUSCLE sequence alignment of the IG1-intron sequences from A. queenslandica and C. tellata. In all alignments, black background indicates identical nucleotides or residues in >50% of the sequences, grey background indicates conservative substitutions, and a white background indicates that the position is conserved in <50% of the sequences. Code names are as in Table 1 with the exception of Oc for Oryctolagus cuniculus and Bt for Bos taurus in (e)