MBB 222 Lecture Notes - Lecture 29: Tandemly Arrayed Genes, Rna Polymerase Iii, 5.8S Ribosomal Rna
20 Dec 2018
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Makes 3 rrnas: 18s, 5. 8s and 28s (s is for svedbergs, named for how the individual rnas sediment during ultracentrifugation) All 3 rrnas are transcribed as a single 45s precursor rna (~13,000 nt long) 45s precursor is cleaved during ribosome assembly - multi-step processing - occurs in the nucleolus. This gene structure ensures that the subunits are always made in equal numbers. Rrna genes are repeated in tandem arrays of ~100-500 copies per cell in most eukaryotes. Rna polymerase iii largest and most complex of the rnaps: 14 subunits, 700 kda synthesizes 5s rrna and trnas in nucleoplasm (i. e. , in nucleus but outside of the nucleolus) 500-20,000 copies of 5s rrna gene in cell - reflect huge number of ribosomes needed transcribes genes - 5s rrna and all trnas - that share certain features: small, do not encode proteins. In eukaryotes, mrna is the key to cell specialization/adaptation. ), timing (when to express?) and location (which cells to express in?).
