( ( If ( we ( assume ( ( the hypothesis ) ( of ( ( the ( early ( ` ( RNA ( world ' ) ) ) ) ) ( containing ( ( ( RNA ( -LRB- ( ribozyme -RRB- ) ) ) ( rather than ) ) ( protein catalysts ) ) ) ) ) ) ) ) ) ( , ( ( the ( present ( day ( RNA-catalysed reactions ) ) ) ) ( ( ( could then ) ( be ( considered ( as ( ( ancestral ( to ( ( similar reactions ) ( that ( have become ) ) ) ) ) protein-dependent ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (PRP we)) (VP (VBP assume) (NP (NP (DT the) (NNS hypothesis)) (PP (IN of) (NP (NP (DT the) (JJ early) (`` `) (JJ RNA) (NN world) ('' ')) (VP (VBG containing) (NP (NP (NNP RNA) (-LRB- -LRB-) (NN ribozyme) (-RRB- -RRB-)) (CONJP (RB rather) (IN than)) (NP (NN protein) (NNS catalysts)))))))))) (, ,) (NP (DT the) (JJ present) (NN day) (JJ RNA-catalysed) (NNS reactions)) (VP (MD could) (RB then) (VP (VB be) (VP (VBN considered) (PP (IN as) (NP (ADJP (JJ ancestral) (PP (TO to) (NP (NP (JJ similar) (NNS reactions)) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (VP (VBN become)))))))) (NN protein-dependent)))))) (. .)))
If we assume the hypothesis of the early 'RNA world' containing RNA (ribozyme) rather than protein catalysts, the present day RNA-catalysed reactions could then be considered as ancestral to similar reactions that have become protein-dependent.
(ROOT (S (NP (NP (DT The) (NN discovery)) (PP (IN of) (NP (NNS ribozymes)))) (VP (VBD nullified) (NP (DT the) (NN idea)) (SBAR (IN that) (S (NP (DT all) (JJ biological) (NNS catalysts)) (VP (VBP are) (NP (NNS proteins)))))) (. .)))