# Glossary

## Motif regular expression

Motif regular expression is a notation commonly used for representing motifs of amino acids or nucleotides. The following conventions are used for motif regular expression:

• Each character, written by itself, denotes a specific amino acid or nucleotide;
• {X} denotes that any amino acid or nucleotide may be used except for 'X';
• [XY] denotes that either 'X' or 'Y' may be used;
• The question mark symbol ('?') denotes that the previous item may or may not appear;

Thus, the amino acid pattern "AR[ND]C?E" encompasses the four protein strings "ARNCE", "ARDCE", "ARNE", and "ARDE"; the DNA pattern "CC{T}AG" encompasses the three DNA strings "CCAAG", "CCCAG", and "CCGAG".