Amino acids domain duplication

Structural analysis of N-24 based on amino acid sequence (derived from its cDNA sequence) revealed some very interesting features. The finding that exons 2, 3 and 4 represent the same repeat sequence has led to the suggestion that this repeated domain may have been generated by duplication of an insertion sequence (Katinakis Verma, 1985). The first and last exons are unique and contain hydrophobic domains. While the first hydrophobic domain at the amino-terminal seems to act as a signal sequence, the hydrophobic domain in the last exon may act as a mem-... 

RND is a large ubiquitous superfamiiy of transporters with representations in all domains of life. Composed typicahy of about 1000 amino-acid residues, they are arranged as 12 transmembrane hehces proteins with two large hydrophilic extra-cytoplasmic loops between hehces 1 and 2 and hehces 7 and 8. It has been postulated that these proteins developed from an internal gene duplication event. The members of the RND family are also secondary active transporters that catalyze the proton-motive-force driven transport of a range of substrates, including hydrophobic drugs, bile salts, fatty acids, heavy metals, and more (22). 

TBP sequences are available from the NCBI server (www.ncbi.nlm.nih.gov/) for organisms representing archaea and the four kingdoms of eukarya. In all cases, the amino acid sequences contain a conserved C-terminal domain of 180 amino acids, and a variable N-terminus, ranging from 1 to 172 residues. The C-terminal domain appears to have arisen by duplication of an ancestor protein before the separation of archaea and eukarya, dividing this domain in two subdomains with -40% identity in sequence [1]. 

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