pattern matching problem

[raouljp@libero.it]

hi,
i need to find a pattern  in a set of sequences.
The pattern is like this one:

AATTCNATNCAACGCGAAGA

N is a base which was not be indetifyed.

regexp =  ajStrNewC("AATTCNATNCAACGCGAAGA");

match = embPatPosSeqMatchFind( seqCurr, regexp );

where seqCurr is a generic sequence of the set.
This is made for all the seqset;
the problem is, I get the match substrings from all analyzed sequences and this
 is the result :
AATTCGATGCAACGCGAAGA

"N"  seems to be a jolly char.
I need an exact match but, how  ?

by R.J.P.B.