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Spot 42 RNA
Spot 42 (''spf'' ) RNA is a regulatory non-coding bacterial small RNA encoded by the spf (spot forty-two) gene. ''Spf'' is found in gammaproteobacteria and the majority of experimental work on Spot42 has been performed in ''Escherichia coli'' and recently in ''Aliivibrio salmonicida''. In the cell Spot42 plays essential roles as a regulator in carbohydrate metabolism and uptake, and its expression is activated by glucose, and inhibited by the cAMP-CRP complex.
The sRNA is transcribed from a separate promoter and binds to messenger RNA targets through imperfect base pairing. The half-life of Spot42 ''in vivo'' is 12 to 13 minutes at 37 °C.〔 When grown in media supplemented with glucose, each cell contains 100-200 Spot42 copies. The corresponding level is however reduced 3-4-fold when cells are grown in succinate or when cAMP is added to cells grown in glucose.〔
==Discovery==
Spot42 was first described in 1973 as an unstable RNA species of 109 nucleotides in ''Escherichia coli''. It was discovered by polyacrylamide gel electrophoresis and 2-D fingerprinting in an attempt to study the accumulation of small RNAs in ''E. coli'' during amino acid starvation.〔〔 In these experiments the electrophoretic mobility of Spot42 was similar to that of 5S rRNA. In 1979 Spot42 was found to accumulate under growth in the presence of glucose (i.e., when adenosine 3′,5′-cyclic monophosphate (cAMP) is low). During growth with a non-glucose carbon source (i.e., when cAMP concentrations are high) the Spot42 concentrations were found to be significantly lower.〔
Later experiments showed that over-expression of Spot42 (~10 fold increase) resulted in impaired growth and lowered ability to adapt to shifts to richer media. Further, shift from glucose to succinate as the carbon source resulted in a long lag period and slow growth rate. It was also stated that the reason for the abnormal responses was caused by an elevated number of excessive Spot42 RNA gene products rather than excess of the gene itself. A deletion study of spf in ''E. coli'' cells resulted in viable spf null mutants, which indicates that Spot42 is non-essential, at least under controlled lab conditions.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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