Identification of selenoproteins in the genome of the marine alga emiliania huxleyi

Organisms from each of the three domains of life, including the cosmopolitan unicellular marine alga Emiliania huxleyi, require the trace element selenium for growth:~ Selenium is incorporated into the active site of select proteins, known as selenoproteins, in the form of the 21st amino acid selenocysteine (Sec). Although the function of many selenoproteins remains unknown, many selenoproteins are oxidoreductases involved in redox homeostasis and anti-oxidant defense systems. We have performed a genome-wide analysis of E. huxleyi 's selenoproteins using two approaches. The first approach was to use a BLAST search to identify selenoproteins based on homology, and the second approach was to identify novel selenoproteins using a computational algorithm and a ribonucleoprotein immunoprecipitation (RIP) procedure. Although the RIP procedure did not yield meaningful results, a total of 49 selenoproteins belonging to 19 protein families were identified based on homology, and 22 candidate selenoproteins containing motifs were identified using a computational algorithm. Real time R T-PCR was used to analyze the expression of a subset of selenoproteins under various physiological stress conditions and demonstrated no uniform expression pattern suggesting that these proteins assume several different functional roles in the cell in addition to serving as anti-oxidants.