( ( The cyclins ) ( ( ( are periodically ) ( expressed ( ( ( during ( the ( cell cycle ) ) ) and ) ( upon ( ( ( binding ( to ( a ( CDK induce ) ) ) ) ( structural rearrangements ) ) ( that ( ( ( ( are both ) ( necessary ( for ( CDK ( catalytic activity ) ) ) ) ) and ) ( also ( help ( to ( determine ( its ( substrate specificity ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS cyclins)) (VP (VBP are) (ADVP (RB periodically)) (VP (VBN expressed) (PP (PP (IN during) (NP (DT the) (NN cell) (NN cycle))) (CC and) (PP (IN upon) (NP (NP (ADJP (JJ binding) (PP (TO to) (NP (DT a) (NNP CDK) (NNP induce)))) (JJ structural) (NNS rearrangements)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBP are) (DT both) (ADJP (JJ necessary) (PP (IN for) (NP (NNP CDK) (JJ catalytic) (NN activity))))) (CC and) (VP (ADVP (RB also)) (VBP help) (S (VP (TO to) (VP (VB determine) (NP (PRP$ its) (JJ substrate) (NN specificity)))))))))))))) (. .)))
The cyclins are periodically expressed during the cell cycle and upon binding to a CDK induce structural rearrangements that are both necessary for CDK catalytic activity and also help to determine its substrate specificity.
(ROOT (S (NP (NNS Cyclins)) (VP (VB regulate) (NP (DT the) (NN cell) (NN cycle)) (ADVP (RB only)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP are) (ADJP (RB tightly) (VBN bound) (PP (TO to) (NP (NNS cdks)))))))) (. .)))