Is top-posting allowed here? I believe NCBI does this as well. I recall talking to them about this when I visited their facilities once. Have you tried emailing ncbi-helpdesk? Someone their should be able to tell you what parameters you need to use to calculate the correct e-value. bl2seq allows you to set a theoretical db size, so I'm sure blast will allow you to as well. Ryan > Hi Daniel, > It is non-trivial to get correct effective database sizes > with NCBI BLAST, as it involves processing both query > sequences and database sequences. You're best bet is to use a > package that can split the databases and return correct > e-values. mpiBLAST is one, but dBlast is another if for some > unfathomable reason you don't like mpiBLAST. > However, depending on what you're doing, e-value differences > may not matter. In my personal opinion, there is no > difference between e-36 and e-40, so the differences you are > talking about are negligible. -Lucas > > On Tuesday, November 21, 2006 at 15:41 -0800, Daniel Xavier > de Sousa wrote: > > > > > > Hi for all, > > > > I need some help about Parallel BLAST. I will bee happy if > anyone help > > me. > > I have worked with parallel BLAST using split database. > > > > I don?t have problem to execute on part of database and statistics > > values when use WUBLAST, because use DBRECMAX and DBRECMIN > > parameters and I execute Blast like virtual split database, > get just > > the piece of all database, and the e-value get right. > > > > But I really want do everything work in NCBI_BLAST. I know the > > solution of mpiBLAST and the list of GI number file. But, these > > solutions aren?t so good. The first because the source of > BLAST have > > to change. And the second, because require that you use GI > numbers in > > the FASTA identifier. > > > > So, my question is: > > > > 1) Somebody > > knows some else solution to run process blast on split > database, and > > not changes the e-value with relation to run whole database? > > > > If not, the difference between e-value with whole database > and part of > > database (using the parameter ?z and ?Y of ncbi_blast) is very > > important? > > > > Example, I processed one sequence with whole database and > just part of > > database, using parameter ?z, the result was: > > > > (evalue)NR > (evalue) NR/2 using ?z > > SeqQuery Seq1DB 4e-66 > 6e-66 > > SeqQuery Seq2DB 4e-38 > 5e-38 > > > > This difference is relevant? > > Thanks, > > > > Daniel Xavier ? PUC ? Rio de Janeiro - Brazil > > > ------------------------------