nucleolar organizer

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nucleolar organizer A segment of a chromosome of a eukaryotic cell containing genes that encode ribosomal RNA. In the nondividing cell it is associated with the nucleolus in the assembly of ribosomes. The nucleolar organizer consists of numerous tandem repeats of a single gene (see tandem array); each repeat is transcribed simultaneously to form multiple copies of a precursor RNA molecule containing all the larger ribosomal RNA subunits.

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