Structures of variable diameter visible in the nucleoplasm by electron microscopy, mainly observed near the border of condensed chromatin. The fibrils are enriched in RNA, and are believed to be sites of pre-mRNA splicing and polyadenylylation representing the in situ form of nascent transcripts. [PMID:14731598]
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C5: Ontology GO: Gene Ontology GO:CC: GO Cellular Component