Custom codons come in threes, fours, and fives.

In a laboratory coselection of reporter messages containing a single randomized essential two-, four-, five-, or six-base "codon" with suppressor tRNA(Ser) libraries whose members possessed randomized anticodon loops of varying sizes, only four- and five-base "codon-anticodon" interactions survived. These suppressor tRNAs accomplish +1 and -1 frameshift suppression, suggesting biological significance. They also display some properties common to serine tRNAs; such properties include a modest excess of Ser anticodons that might assist tRNA charging.