Factor for inversion stimulation-dependent growth rate regulation of serine and threonine tRNA species

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.