The prototypic sequence (many variations exist) is serine-lysine-leucine (-SKL in the one-letter amino acid code).
A few peroxisomal matrix proteins have a different, and less conserved sequence, at their amino termini.
"PEX" refers to a group of genes that were identified as being important for peroxisomal synthesis.
The numerical attributions, such as PEX5, generally refer to the order in which they were first discovered.
[2] One of these usually is a cluster of basic amino acids (arginines and lysines) within a loop of protein (i.e., between membrane spans) that will face the matrix.