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Ribosomal
RNA is transcribed as a 45S precursor RNA,
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synthesized
in the nucleolus by polI from thousands of
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copies
of the gene.
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The
45S precursor (13,000 nt)is processed into 3
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smaller
RNAs 28S (5000 nt), 18S (2000 nt) and 5.8S
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(160
nt)
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The
5S subunit is synthesized by polIII from a cluster of
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2000
genes located separately from the other ribosomal
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genes
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Some
80 proteins associate with the rRNAs to make up
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complete
ribosome.
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Small
ribosomal subunit (40S) contains 18S rRNA
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while
the large 60S subunit contains the remaining
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rRNAs
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