Comparison of the conceptual amino acid sequences of nocturnin homologues from chicken (CNOC), cow (BNOC), rat, (RNOC), Xenopus (XNOC), mouse (MNOC), human (hNoc) and Drosophila (DNOC). Sequences were analyzed using the Clustal W Alignment procedure. Gaps indicated with dots are inserted to achieve optimum alignment. Dark gray and light gray highlights indicate amino acid identities and similarities respectively. The horizontal bar marks the position of the heptad leucine repeat in Xenopus and the asterisks indicate the position of the leucines. The positions of introns 1 and 2 based on the Xenopus gene  are indicated by arrows. Note that both mouse  and human (from data in public databases of the National Library of Medicine) appear to have a similar gene structure based on 3 exons. The XNOC sequence is from GenBank accession number U74761, HNOC is from NP036250.1 , and DNOC is from AAF54601.1 . Our complete mNoc cDNA from retina (accession number AF199491) has the same coding sequence as that reported earlier from liver [38,39]. The cNoc (AF199498), bNoc (AF199497), and rNoc (AF199495) partial sequences are from PCR amplified DNA segments.