Marine Iguana Class I Figure 4. Class I phylogenetic reconstruction using a-3 (exon 4) sequence data from the major vertebrate groups. The top number at each node is the Bayesian posterior distribution value supporting the topology displayed. The middle and bottom numbers are bootstrap values from maximum likelihood and neighbor joining searches respectively. Branch lengths are represented as expected number of substitutions per site and were inferred along with topology in the Bayesian analysis. doi:10.1371/journal.pone.0002859.g004 found in a pseudogene. There are also no stop codons in any of the exon 3 UA sequences from other iguanine species. The presence of a polyadenylation signal in the 39 UTR is essential for the transcription of a functional gene. While neither of the canonical polyadenylation signals (AATAAA or ATTAAA) were found in the Amcr-UA cDNA sequence, several alternative sites were identified, including ATAAA, which is known from fish [41], and AAGAAA, from humans [31]. Moreover, Beaudoing et al. [30] showed that the signal sequence and its position from the poly(A) region vary greatly within the human genome. PLoS ONE | www.plosone.org 8 August 2008 | Volume 3 | Issue 8 | e2859