passages.id: split_4_test_472_passage
passages.type: progene_text
passages.text: The yeast nucleolar protein Rrp5p is the only known trans - acting factor that is essential for the synthesis of both 18S rRNA and the major , short form of 5.8S ( 5.8Ss ) rRNA , which were thought to be produced in two independent sets of pre - rRNA processing reactions .