Abstract
We have previously shown that the accumulation of 20 tRNA species in Escherichia coli is individually regulated as a function of cellular growth rate. We have also reported that the growth rate regulation of some but not all tRNA species is dependent on the activity of the factor for inversion stimulation (FIS). In present work, we studied the growth rate regulation of the serine- and threonine-accepting tRNA families. We show that the levels of tRNA(3Thr), tRNA(3Ser), tRNA(2Thr), tRNA(3Thr), and tRNA(4Thr) are reduced in fis cells as the growth rate increases. The accumulation of these tRNA species is reduced 2-5-fold at the fastest bacterial growth rate. The strongest effect is observed for the two minor tRNA species; tRNA(2Ser) and tRNA(2Thr). In contrast, we find that the accumulation of tRNA(1Ser), tRNA(5Ser), and tRNA(1Thr) is similar in wild type and fis bacteria. The data presented provide further evidence for the suggestion that FIS is a stimulating factor that is involved, directly or indirectly, in the high expression level of some tRNA genes at fast bacterial growth rates.
Highlights
IntroductionDeletion of the genes that encode the two ppGpp synthetases results in a bacterium (reIA, spoT) that, albeit with a slower growth rate, regulates stable RNA synthesis in a normal growth rate-dependent manner [7]
We found that the growth rate-dependent expression of arginine, methionine, and leucine-accepting tRNA species can be divided into four groups pertaining to the effect of deleting the {is gene [17]
The accumulation rate of one group of tRNA species decreases in the absence of FIS
Summary
Deletion of the genes that encode the two ppGpp synthetases results in a bacterium (reIA, spoT) that, albeit with a slower growth rate, regulates stable RNA synthesis in a normal growth rate-dependent manner [7] This suggests either that ppGpp is not involved in the growth rate control or alternatively that some other regulatory mechanisms take over in the absence of ppGpp. This suggests either that ppGpp is not involved in the growth rate control or alternatively that some other regulatory mechanisms take over in the absence of ppGpp One such mode of regulation has been described as ribosomal feedback inhibition [8]. Expression of the other three tRNA species are identical in wild type and fis bacteria These data provide support for the suggestion that the FIS protein is involved in the high expression level of many tRNA genes at fast bacterial growth rates
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