My understanding of .msk files is that they serve to mask out the est sequences you don't want to search. More explicitly, if you download all the est sequences in the preformatted db and if you only want to search est_others, this allows you to have a single est db but have virtual dbs for est_others as described in the .nal and .msk files. In principle this sounds fine until you try and get it to work for segmented dbs on a cluster. dave On Thursday, September 18, 2003, at 12:01 PM, Tim Harsch wrote: > And what are the *.MSK files?? For instance if you take a look at > est_others.tar.gz, it is very small and there are only *.nal and *.msk > files > in there. Is the msk file used by the blast standalone as an > instruction as > to how to add new data into the database when blasting, or is it an > instruction to fmerge for putting them together or what?