In addition to these biological tools, certain naturally observed configurations of DNA (genes, promoters, enhancers, repressors) and the associated machinery itself are referred to as an expression system.
Ademais destas ferramentas biolóxicas, na natureza obsérvanse certas configuracións do ADN (xenes, promotores, amplificadores, represores) e a propia maquinaria asociada, que se denominan sistema de expresión.