Run PSI-BLAST on query
To broaden the set of sequences representing the query family, the input 
MSA (or single sequence) can be used to initiate PSI-BLAST search on UNIREF
database. The sequences detected by PSI-BLAST are filtered by user-specified
E-value, coverage of the query length, and sequence identity to the query.
The resulting PSI-BLAST alignment is submitted to COMPASS as a query.

By default, this PSI-BLAST search is performed only if query is 
a single sequence. If multiple sequence alignment is submitted, COMPASS will
use it 'as is', unless the user specifically requires the initial PSI-BLAST
search. See 'Run PSI-BLAST if input is an alignment'.