The crocodilian mitochondrial control region: general structure, conserved sequences, and evolutionary implications.

We present the first comprehensive analysis of the crocodilian control region. We have analyzed sequences from all three families of Crocodylia (Crocodylidae, Gavialidae, Alligatoridae), incorporating all genera except Paleosuchus and Melanosuchus. Within the control region of other vertebrates, several sequence motifs and their order appear to be conserved. Herein, we compare aligned crocodilian D-loop sequences to homologous sequences from other vertebrates ranging from fish to birds. Among other findings, we have discovered that while domain I tends to be shorter than the same region in mammals and birds, it contains sequences similar in structure to both the goose-hairpin and termination associated sequences (TAS). Domain II is highly conservative with regard to size among the taxa examined and contains several of the conserved sequence boxes characterized in other vertebrates. Domain III contains several interesting sequence motifs including tandemly repeated sequences, a long poly-A region in the Crocodylidae, and possible bidirection promoter sequences.