Fibrillarin is a component of a nucleolar small nuclear ribonucleoprotein (snRNP) particle thought to participate in the first step in processing preribosomal RNA. Fibrillarin is a crucial nonhistone protein predominantly located in the fibrillar region of the nucleolus, specifically within the dense fibrillar and fibrillar center regions. Fibrillarin′s localization is vital for ribosome biogenesis, playing a key role in processing ribosomal RNA (rRNA) transcripts. During the cell cycle, Fibrillarin serves as an early marker for nucleolus formation in telophase, highlighting Fibrillarin′s importance in cellular division and nucleolar reassembly. Fibrillarin′s structure features an RNA-binding domain and an RNP consensus sequence, facilitating interaction with U3 small nucleolar RNA, further underscoring Fibrillarin′s essential function in rRNA maturation.