The Site Of Pre-rRNA Processing During The Cell Cycle In Allium Sativum

The nucleolus is the domain in which transcription and assembly of ribosomes take place in eukaryotes, it is composed of three basic subcompartments: fibrillar centers (FC), dense fibrillar component (DFC) and granular component (GC). Processing of pre-rRNA is one of the major events taking place in the nucleolus. Fibrillarin and U3 snoRNA are two important rRNA spliceosomal factors. They are suggested to be essential in the first cleavage step of the 5'ETS sequence in the processing of pre-rRNA. Identification of fibrillarin and U3 in the nucleolus provides a piece of indirect evidence for pre-rRNA processing site and transportation of processing products. In this report, subnucleolar distribution of fibrillarin and U3 snoRNA in the nucleolus of Allium Sativum were studied by in situ hybridization and immunoelectron microscopy during cell cycle. So we can get the information of pre-rRNA processing site in the cell cycle. The results are as follow:1. In the nucleolus, fibrillarin was mainly localized in DFC regions, especially where it near the FCs. The GC were slightly labeled, but FC were unlabelled. In G2 phase nucleoli, the fibrillain labelling signals come to a head.2. In the nucleolus, U3 snoRNA localized in DFC regions, especially where it abuts the FCs. The GC were a little labeled, but FC were unlabelled. In S and G2 phase, the U3 snoRNA labeling signals were highly enriched in DFC.3. The fibrillarin and U3 snoRNA labelling experiments provide two pieces of indirect evidences indicated that pre-rRNA splicing took place in the regions of DFC and GC, and pre-rRNA processing was more active in S and G2 phase.