Prions are units of propagation of an altered state of a protein or proteins; 
prions can propagate from organism to organism, through cooption of other 
protein copies. Prions contain no necessary nucleic acids, and are important 
both as both pathogenic agents, and as a potential force in epigenetic 
phenomena. The original prions were derived from a misfolded form of the 
mammalian Prion Protein PrP. Infection by these prions causes neurodegenerative 
diseases. Other prions cause non-Mendelian inheritance in budding yeast, and 
sometimes act as diseases of yeast. We report the bioinformatic construction of 
the PrionHome, a database of >2000 prion-related sequences. The data was 
collated from various public and private resources and filtered for redundancy. 
The data was then processed according to a transparent classification system of 
prionogenic sequences (i.e., sequences that can make prions), prionoids (i.e., 
proteins that propagate like prions between individual cells), and other 
prion-related phenomena. There are eight PrionHome classifications for 
sequences. The first four classifications are derived from experimental 
observations: prionogenic sequences, prionoids, other prion-related phenomena, 
and prion interactors. The second four classifications are derived from sequence 
analysis: orthologs, paralogs, pseudogenes, and candidate-prionogenic sequences. 
Database entries list: supporting information for PrionHome classifications, 
prion-determinant areas (where relevant), and disordered and 
compositionally-biased regions. Also included are literature references for the 
PrionHome classifications, transcripts and genomic coordinates, and structural 
data (including comparative models made for the PrionHome from manually curated 
alignments). We provide database usage examples for both vertebrate and fungal 
prion contexts. Using the database data, we have performed a detailed analysis 
of the compositional biases in known budding-yeast prionogenic sequences, 
showing that the only abundant bias pattern is for asparagine bias with 
subsidiary serine bias. We anticipate that this database will be a useful 
experimental aid and reference resource. It is freely available at: 
http://libaio.biol.mcgill.ca/prion.