This directory is often installed in the location /usr/ncbi/blast/filter.
If a different location is desired, use the BLASTFILTER environment variable
to direct the BLAST programs where to look.

The filter directory should contain executables used to filter query sequences
of any low-complexity regions (or any other regions of one's design).  These
executables are invoked indirectly using the "filter=" option of the BLAST
programs.  Filter programs must be capable of reading FASTA format sequences
and writing their results in FASTA format.  Filter programs are maintained
separately from the BLAST programs, so they may be updated independently.

Typical filters that the BLAST programs know about are "seg" (Wootton and
Federhen) and "xnu" (Claverie and States).

Source code for seg is available at URL ftp://ncbi.nlm.nih.gov/pub/seg
or ftp://blast.wustl.edu/pub/seg

Source code for xnu is available at URL ftp://ncbi.nlm.nih.gov/pub/jmc/xnu
or ftp://blast.wustl.edu/pub/xnu


