Table 2.

Inventory of mammalian mitochondrial tRNA modifications

Pos.	Mod.	mt-tRNA species	Enzyme(s)	Disease associations	Refs.
6	m2G	Asp	THUMPD2 or THUMPD3		[91]
9	m1A	Ala, Arg, Asp, Asn, Glu, Gly, His, LeuCUN, Lys, Phe, Pro, Thr, Trp, Val,	MRPP1, MRPP2	HSD10 disease	[76, 80]
	m1G	Cys, Gln, Ile, LeuUUR, Tyr	MRPP1, MRPP2	HSD10 disease	[76, 80]
10	m2G	Ala, Asn, Phe, Gly, His, LeuUUR, LeuCUN, Lys, Pro, Trp, Tyr, Val	TRMT11		[92]
16	m1A	Arg	?		[84]
20	D	LeuUUR, LeuCUN, SerUCN	DUS2	Lung cancer	[93, 94]
26	m2G	Ala, Glu, LeuUUR	?
	${\text{m}}^2{}_2\text{G}$	Ile	TRMT1	Intellectual disability	[86–88]
27	ψ	Asn, Asp, Cys, His, Ile, LeuUUR, LeuCUN, Met, Pro, Val	PUS1	MLASA	[98, 99]
27a	ψ	SerUCN	PUS1	MLASA	[98]
28	ψ	Ala, Asn, Cys, Glu, LeuCUN, Lys, SerUCN, Tyr	PUS1	MLASA	[98, 99]
29	ψ	SerUCN	PUS1		[98]
31	ψ	Asp, LeuCUN	RPUSD1		[100]
32	ψ	Cys, Val	RPUSD2		[101]
	m3C	SerUCN, Thr	?
34	τm5U	Gln, Glu, LeuUUR, Lys, Trp	GTPBP3, MTO1	MELAS, MERRF, HCLA	[118, 119, 124, 125]
	τm5s2U	Gln, Glu, Lys	GTPBP3, MTO1, MTU1	RIRCD, DEAF	[120, 121, 127–131]
	f5C	Met	NSUN3, ABH1	MM, developmental disability, microcephaly, failure to thrive, external ophthalmoplegia, convergence nystagmus	[45, 110, 111]
	Q	Asn, Asp, His, Tyr	QTRTD1	Morris hepatoma	[107]
37	t6A	Asn, Ile, Lys, SerAGY, Thr	YRDC, OSGEPL1		[135–137]
	i6A	Cys, Phe, SerUCN, Trp, Tyr	TRIT1	Encephalopathy and myoclonic epilepsy, lung cancer	[140, 143]
	ms2i6A	Phe, SerUCN, Trp, Tyr	TRIT1, CDK5RAP1	Encephalopathy and myoclonic epilepsy, lung cancer	[143, 144, 146]
	m1G	Gln, LeuCUN, Pro	TRMT5	Mitochondrial myopathy, lactic acidosis	[132, 134]
39	ψ	Ala, Arg, Cys, Gln, Gly, His, LeuUUR, Phe, Tyr	PUS3		[102]
40	ψ	Gln, Glu	PUS3		[102]
48	m5C	Asn, LeuUUR, Trp	?
49	m5C	Glu, SerAGY	?
50	ψ	Met	?
55	ψ	Gln, Glu, SerUCN, Tyr	TRUB2		[58, 103]
57	ψ	Ala	?
58	m1A	Cys, Glu, Ile, Lys, LeuUUR, SerUCN	TRMT61B		[82]
67	ψ	Thr	PUS1		[98]
72	m5C	Thr	?

The positions (Pos.) of modifications (Mod.) detected in bovine mt-tRNA species, according to [74] or the individual references given, are shown. Enzymes demonstrated to be involved in installing these modifications in mammals are shown in bold and predicted enzymes (based on homology to the enzymes responsible for these modifications in other species) are given in italics, along with disease associations arising from mutations in the known or predicted modification enzymes and references (Refs.) where applicable

DEAF maternally inherited deafness, HCLA hypertrophic cardiomyopathy and lactic acidosis, MELAS mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes, MERRF myoclonic epilepsy with ragged red fibres, MLASA mitochondrial myopathy, lactic acidosis and sideroblastic anemia, MM mitochondrial myopathy, RIRCD reversible infantile respiratory chain deficiency