1. Experimentally identified phosphorylation sites. 
2. The experimental phosphorylation sites were taken from several major databases, including PhosphoPep, Phospho.ELM, SysPTM, PhosphoSitePlus and HPRD. The literature mining was also carried out to add additional phosphorylation sites. 
3. All phosphorylated substrates were mapped to the UniProt database (http://www.uniprot.org/). 
4. Five organisms including Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Mus musculus and Homo sapiens were considered.
5. Redundant data were cleared. 
6. Data format: the ist column, UniProt ID of phosphorylated protein; the 2nd column, protein sequence of phosphorylated protein; the 3rd column, phosphorylated position; the 4th column, phosphorylated residue type; the 5th column, source of phosphorylation sites. The data format was adopted from the Phospho.ELM database. 
7. Files:
(1) SC.elm: budding yeast phosphorylation sites
(2) CE.elm: nematode phosphorylation sites
(3) DM.elm: fruit fly phosphorylation sites
(4) MM.elm: mouse phosphorylation sites
(5) HS.elm: human phosphorylation sites
8. Last updated, April 16, 2010.
