the difference between non-canonical and canonical poly(a) polymerases is that canonical polymerases help in maintaining mrnas and its activity is regulated by a specific sequence in the mrna while polyadenylation of non-canonical polymerases uses a different regulated sequence in the rna and specifies rnas for degeneration or processing. canonical polymerases belong to dna polymerase β superfamily whereas non-canonical polymerases belong to cid1 family, another main difference is the length of the poly(a) tail; canonical polymerases can add many adenylates thus the rna produced has longer poly(a) tails while non-canonical polymerases on the other hand can produce rnas with shorter length of poly(a) tails as they can add only few adenylates.