Nucleic Acids Research Advance Access originally published online on July 11, 2007
Nucleic Acids Research 2007 35(15):4952-4963; doi:10.1093/nar/gkm514
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Nucleic Acids Research, 2007, Vol. 35, No. 15 4952-4963
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Genomics |
High content of proteins containing 21st and 22nd amino acids, selenocysteine and pyrrolysine, in a symbiotic deltaproteobacterium of gutless worm Olavius algarvensis
Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA
*To whom correspondence should be addressed. Tel: +1 402 472 4948; Fax: +1 402 472 7842; Email: vgladyshev1{at}unl.edu
Received May 24, 2007. Revised June 14, 2007. Accepted June 14, 2007.
Selenocysteine (Sec) and pyrrolysine (Pyl) are rare amino acids that are cotranslationally inserted into proteins and known as the 21st and 22nd amino acids in the genetic code. Sec and Pyl are encoded by UGA and UAG codons, respectively, which normally serve as stop signals. Herein, we report on unusually large selenoproteomes and pyrroproteomes in a symbiont metagenomic dataset of a marine gutless worm, Olavius algarvensis. We identified 99 selenoprotein genes that clustered into 30 families, including 17 new selenoprotein genes that belong to six families. In addition, several Pyl-containing proteins were identified in this dataset. Most selenoproteins and Pyl-containing proteins were present in a single deltaproteobacterium, 
1 symbiont, which contained the largest number of both selenoproteins and Pyl-containing proteins of any organism reported to date. Our data contrast with the previous observations that symbionts and host-associated bacteria either lose Sec utilization or possess a limited number of selenoproteins, and suggest that the environment in the gutless worm promotes Sec and Pyl utilization. Anaerobic conditions and consistent selenium supply might be the factors that support the use of amino acids that extend the genetic code.