The Signal Recognition Particle Database (SRPDB) at http://psyche.uthct.edu/dbs/SRPDB/SRPDB.html and http://bio.lundberg.gu.se/dbs/SRPDB/SRPDB. html assists in the better understanding of the structure and function of the signal recognition particle (SRP), a ribonucleoprotein complex that recognizes signal sequences as they emerge from the ribosome. SRPDB provides alphabetically and phylogenetically ordered lists of SRP RNA and SRP protein sequences. The SRP RNA alignment emphasizes base pairs supported by comparative sequence analysis to derive accurate SRP RNA secondary structures for each species. This release includes a total of 181 SRP RNA sequences, 7 protein SRP9, 11 SRP14, 31 SRP19, 113 SRP54 (Ffh), 9 SRP68 and 12 SRP72 sequences. There are 44 new sequences of the SRP receptor alpha subunit and its FtsY homolog (a total of 99 entries). Additional data are provided for polypeptides with established or potential roles in SRP-mediated protein targeting, such as the beta subunit o...