Figure 4.

Conservation of ancestral gene clusters in Leptosira and other UTC algal cpDNAs. Black boxes represent the 89 genes found in the 24 clusters shared by Mesostigma and Nephroselmis cpDNAs as well as the genes in UTC algal cpDNAs that have retained the same order as those in these ancestral clusters. For each genome, the set of genes making up each of the identified clusters (either an intact or a fragmented ancestral cluster) is shown as black boxes connected by a horizontal line. Black boxes that are contiguous but are unlinked indicate that the corresponding genes are not adjacent on the genome. Grey boxes denote individual genes that have been relocated on the chloroplast genome; open boxes denote genes that have disappeared from the chloroplast genome. Although the rpl22 gene is missing from Nephroselmis cpDNA, it is shown as belonging to the ribosomal protein cluster equivalent to the contiguous S10, spc and α operons of Escherichia coli because it is present in this cluster in the cpDNAs of Mesostigma, streptophytes and algae from other lineages. Note also that the psbB cluster of Pseudendoclonium differs from the ancestral cluster by the presence of psbN on the alternate DNA strand.