▁are ▁c oval ently ▁linked ▁to ▁the ▁substr ate . ▁If ▁a ▁mole c ule ▁poss esses ▁the ▁desired ▁lig ase ▁activity , ▁a ▁stre pt avid in ▁matrix ▁can ▁be ▁used ▁to ▁recover ▁the ▁active ▁mole cules . ▁ ▁Lincoln ▁and ▁Joy ce ▁developed ▁an ▁R NA ▁en zym e ▁system ▁capable ▁of ▁self ▁rep lication ▁in ▁about ▁an ▁hour . ▁ ▁By ▁util izing ▁mole cular ▁competition ▁( in ▁vit ro ▁evolution ) ▁of ▁a ▁candidate ▁R NA mi xture , ▁a ▁pair ▁of ▁rib oz ym es ▁emer ged , ▁in ▁which ▁each ▁synth es izes ▁the ▁other ▁by ▁joining ▁synth etic ▁o lig on uc le ot ides , ▁with ▁no ▁protein ▁present . ▁ ▁Although ▁not ▁true ▁catal yst s , ▁the ▁creation ▁of ▁artificial ▁self - cle aving ▁rib os w itch es , ▁term ed ▁apt az ym es , ▁has ▁also ▁been ▁an ▁active ▁area ▁of ▁research . ▁ ▁Rib os w itch es ▁are ▁regul atory ▁R NA ▁mot ifs ▁that ▁change ▁their ▁structure ▁in ▁response ▁to ▁a ▁small ▁mole c ule ▁lig and ▁to ▁reg ulate ▁translation . ▁ ▁While ▁there ▁are ▁many ▁known ▁natural ▁rib os w itch es ▁that ▁bind ▁a ▁wide ▁array ▁of ▁met abol ites ▁and ▁other ▁small ▁organ ic ▁mole cules , ▁only ▁one ▁rib oz yme ▁based ▁on ▁a ▁rib os w itch ▁has ▁been ▁described , ▁gl m S . ▁ ▁Early ▁work ▁in ▁character izing ▁self - cle aving ▁rib os w itch es ▁was