passages.id: split_6_test_2928_passage
passages.type: progene_text
passages.text: Localization of proteins involved in the rRNA transcription ( upstream binding factor [ UBF ] , topoisomerase I , RNA polymerase I [ RNA Pol I ] , and the RNA Pol I - associated factor PAF53 ) and processing ( fibrillarin , nucleophosmin , and nucleolin ) was assessed by immunocytochemistry and confocal laser - scanning microscopy , and mRNA expression was determined by semiquantitative reverse transcription - polymerase chain reaction ( RT - PCR ) .