Table 1.

tRNA modification enzymes that either require an Fe/S cluster or depend on the Nfs desulfurase for activity

Enzymea	Fe/S cluster	Localization	Function
MiaB	Yes	?b	Methyl thiolation at position 37 of tRNAs
Tyw1	Yes	Cytoplasmic	First step of wybutosine biosynthesis at position 37 of tRNAPhe
Urm1, Uba4, Ncs2, Ncs6	?	Cytoplasmic	Thiolation of tRNAGln, tRNAGlu, and tRNALys
Elp3	Yes	Cytoplasmic	Alkylation of tRNAs at position 34
Mtu1	No, but requires Nfs	Mitochondrial	Thiolation of various tRNAs at position 34 and tRNATrp at position 33 in T. brucei

^aVarious potential homologs of these enzymes are found in the T. brucei sequence database

^bIntracellular localization not known