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rdf:type |
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lifeskim:mentions |
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pubmed:issue |
2
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pubmed:dateCreated |
1978-10-25
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pubmed:abstractText |
The metabolism of mRNA from the lactose (lac) operon of Escherichia coli has been studied in ribonuclease (RNase) III-deficient strains (rnc-105). The induction lag for beta-galactosidase from the first gene was twice as long, and enzyme synthesis was reduced 10-fold in one such mutant compared with its isogenic rnc+ sister; in the original mutant strain AB301-105, synthesis of beta-galactosidase was not even detectable, although transduction analysis revealed the presence of a normal lac operon. This defect does not reflect a loss of all lac operon activity galactoside acetyltransferase from the last gene was synthesized even in strain AB301-105 but at a rate several times lower than normal. Hybridization analyses suggested that both the frequency of transcription initiation and the time to transcribe the entire operon are normal in rnc-105 strains. The long induction lag was caused by a longer translation time. This defect led to translational polarity with reduced amounts of distal mRNA to give a population of smaller-sized lac mRNA molecules. All these pleiotropic effects seem to result from RNase III deficiency, since it was possible to select revertants to rnc+ that grew and expressed the lac operon at normal rates. However, the rnc-105 isogenic strains (but not AB301-105) also changed very easily to give a more normal rate of beta-galactosidase synthesis without regaining RNase III activity or a faster growth rate. The basis for this reversion is not known; it may represent a "phenotypic suppression" rather than result from a stable genetic change. Such suppressor effects could account for earlier reports of a noninvolvement of RNase III in mRNA metabolism in deliberately selected lac+ rnc-105 strains. The ribosomes from rnc-105 strains were as competent as ribosomes from rnc+ strains to form translation initiation complexes in vitro. However, per mass, beta-galactosidase mRNA from AB301-105 was at least three times less competent to form initiation complexes than was A19 beta-galactosidase mRNA. RNase III may be important in the normal cell to prepare lac mRNA for translation initiation. A defect at this step could account for all the observed changes in lac expression. A potential target within a secondary structure at the start of the lac mRNA is considered. Expression of many operons may be affected by RNase III activity; gal and trp operon expressions were also abnormal in RNase III- strains.
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pubmed:commentsCorrections |
http://linkedlifedata.com/resource/pubmed/commentcorrection/98520-1088926,
http://linkedlifedata.com/resource/pubmed/commentcorrection/98520-1091644,
http://linkedlifedata.com/resource/pubmed/commentcorrection/98520-1095585,
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http://linkedlifedata.com/resource/pubmed/commentcorrection/98520-765478,
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http://linkedlifedata.com/resource/pubmed/commentcorrection/98520-957436
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pubmed:language |
eng
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pubmed:journal |
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pubmed:citationSubset |
IM
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pubmed:chemical |
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pubmed:status |
MEDLINE
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pubmed:month |
Aug
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pubmed:issn |
0021-9193
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pubmed:author |
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pubmed:issnType |
Print
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pubmed:volume |
135
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
528-41
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pubmed:dateRevised |
2009-11-18
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pubmed:meshHeading |
pubmed-meshheading:98520-Enzyme Induction,
pubmed-meshheading:98520-Escherichia coli,
pubmed-meshheading:98520-Galactose,
pubmed-meshheading:98520-Lactose,
pubmed-meshheading:98520-Operon,
pubmed-meshheading:98520-Protein Biosynthesis,
pubmed-meshheading:98520-RNA, Bacterial,
pubmed-meshheading:98520-RNA, Messenger,
pubmed-meshheading:98520-Ribonucleases,
pubmed-meshheading:98520-Tryptophan,
pubmed-meshheading:98520-beta-Galactosidase
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pubmed:year |
1978
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pubmed:articleTitle |
Altered mRNA metabolism in ribonuclease III-deficient strains of Escherichia coli.
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pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, P.H.S.,
Research Support, U.S. Gov't, Non-P.H.S.
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