Mensur Dlakic said: > Disclaimer: I am no BLAST expert, so some of the things I say below are just > common(ly wrong) sense. > >>Would the difference in e value be more prounounced in the second itteration if >> the first HSP had a low e value? > > I think so. I routinely set E-value lower than h-value for PSI-BLAST iterations > and often see that E-values improve quite a lot for many sequences, though not > necessarily below the h-value so they don't get included in the profile. I can see why this would happen, and why you would want it to happen, But I think that for a single sequence hit the second itteration e-value may misrepresent the actual significance - I guess this is the problem with profile itteration and false +ve hits! >>Is this a reason for including query sequences in the search space? (to track the >> value of self hits)? > > I think that it has to be included, if for no other reason than only to have > something for alignments. That said, I have seen that with some profiles the > query sequence will stop being the best match after a few iterations, meaning > that it'll move down the list a bit. Has this drift been studied in detail? Any refs? Cheers, Dan.