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Feedback Regulation of rRNA and tRNA Synthesis and Accumulation of Free Ribosomes after Conditional Expression of rRNA Genes

Richard L. Gourse, Yutaka Takebe, Robert A. Sharrock and Masayasu Nomura
Proceedings of the National Academy of Sciences of the United States of America
Vol. 82, No. 4 (Feb. 15, 1985), pp. 1069-1073
Stable URL: http://www.jstor.org/stable/25165
Page Count: 5
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Feedback Regulation of rRNA and tRNA Synthesis and Accumulation of Free Ribosomes after Conditional Expression of rRNA Genes
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Abstract

We have constructed a conditional rRNA gene expression system by fusing a plasmid-encoded rrnB operon to the λ PL promoter/operator. It was thereby possible to study the events that lead to the regulation of chromosomal rRNA and tRNA synthesis after overproduction of rRNA. rRNA induction resulted in a 2-fold increase in 30S and 50S free ribosomal subunits, whereas the polysome fraction was unaffected. Overproduction of rRNA and ``free'' ribosomes produced a large repression of rRNA and tRNA synthesis from chromosomal genes and a smaller increase in the concentration of guanosine tetraphosphate. These results lend support to the ribosome feedback regulation model: rRNA and tRNA operons are negatively regulated, either directly or through some intermediate, by free, nontranslating ribosomes.

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