In standard Golden Gate Cloning, the restriction sites from the previous tier construct cannot be reused. To add more genes to the construct, restriction sites of a different Type IIS restriction enzyme need to be added to the destination vector. This can be done using either level 2, or M and P. A variant version of level M and P is also provided by GoldenBraid.
GoldenBraid overcomes the problem of designing numerous destination vectors by having a double loop, which is the "braid," to allow binary assembly of multiple constructs. There are two levels of destination plasmids, level α and level Ω. Each level of plasmids can be used as entry plasmids for the other level of plasmids for multiple times because both levels of plasmids have different Type IIS restriction sites that are in inverted orientation. For counterselection, the two levels of plasmids differ in their antibiotic resistance markers.