( PCNA ( ( ( was originally ) ( identified ( as ( ( an antigen ) ( that ( is ( ( expressed ( in ( ( the nuclei ) ( of cells ) ) ) ) ( during ( ( the ( DNA ( synthesis phase ) ) ) ( of ( the ( cell cycle ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP PCNA)) (VP (VBD was) (ADVP (RB originally)) (VP (VBN identified) (PP (IN as) (NP (NP (DT an) (NN antigen)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (VP (VBN expressed) (PP (IN in) (NP (NP (DT the) (NN nuclei)) (PP (IN of) (NP (NNS cells))))) (PP (IN during) (NP (NP (DT the) (NNP DNA) (NN synthesis) (NN phase)) (PP (IN of) (NP (DT the) (NN cell) (NN cycle))))))))))))) (. .)))
PCNA was originally identified as an antigen that is expressed in the nuclei of cells during the DNA synthesis phase of the cell cycle.
(ROOT (S (PP (IN During) (NP (NP (DT the) (NN synthesis) (NN phase)) (PP (IN in) (NP (DT the) (NN cell) (NN cycle))))) (, ,) (NP (NN dna) (NN replication)) (VP (VBZ occurs)) (. .)))