Table 1.

Example of regulations by tRNA modifications in Bacteria

Organism	Stress	Mod	tRNA	Mod Enzyme	Target protein/codon	Mechanism
Escherichia coli K12	Low iron	ms2i6A37	Ser-UGA	Fe/S dependent Enzyme MiaB Ser-UCA	U ofSer-UCA	Low iron, leads to reduced MiaB activity and lower modification of tRNASer- and to poor translation of uof and fur encoding the negative regulator of the low iron response (reviewed in [90])
	?	i6A37	Leu-UAA	MiaA	RpoS. IraP,Hfq Leu-UUX	MiaA, TrmL and TusA identifies as MOTTs but mechanisms that affects modification levels unknown [104,105]
	?	C/U34m	Leu-C/UAA	TrmL	RpoS Leu-UUX	[105]
	?	s2U34	Leu-UAA	TusA	RpoS Leu-UUX	[105]
	Growth phase	mcmo5U	Pro-UGG	CmoM	?	The ratio of mcmo5U/cmo5U increases clearly during growth phase but the molecular mechanisms are yet to be discovered [106].
Salmonella typhimurium LT2	Low Mg2+	m1G37	Pro-C/G/UGG	Mg2+ dependent enzyme TrmD	MgtL, Pro-CCX	Low Mg2+ leads to reduced TrmD activity and lower modification of tRNAPro that triggers attenuation of the MgtL leader peptide allowing expression of the coupled mgtA transporter gene [107]
Pseudomonas aeruginosa PAO1	H2O2	m7G47	Asp-GUC Phe-GAA	TrmB	KatA and KatB Phe-UUC Asp-GAC	Transcription of trmB is increased under oxidative stress by an unknown mechanism leading to increased translation of the katAB genes [108]
	H2O2	C/U/Am32		TrmJ	OxyR ?	trmJ is essential for a proper expression of katB during H2O2 stress through a modulation of oxyR expression it was not shown that OxyR translation is affected at specific codons [109]
	H2O2	s2C32		TtcA	KatA ?	The expression of TtcA is under the positive control of OxyR. It is postulated but not proven that this leads to increased translation of the catalase gene KatA [110]
Mycobacterium bovis BCG	Low O2	cmo5U34	Thr-UGU	CmoR (BCG_0224)	DosR, Thr-ACG	Reprogramming of tRNA and modification pool switches proteome and allows increased expression of DosR the regulator of the hypoxic response [26].
Salmonella typhimurium LT2 & E. coli K12	UV	s4U	Many	NA	NA	Presence of s4U under UV stress leads to cross-linking of tRNAs and to a translation block similar to stringent response [111,112].