AA	Amino acid sequence comparison.
CE	Coincident expression.
CL	Conserved genome location (synteny).
FC	Functional complementation.
FH	Formation of functional heteropolymers.
IX	Immunological cross-reaction.
NS	Not specified.
NT	Nucleotide sequence comparison.
SI	Similar response to inhibitors.
SL	Similar subcellular location.
SS	Similar substrate specificity.
SU	Similar subunit structure.
XH	Cross-hybridization to same molecular probe.