This protein is also known as sun protein. The reading frame was originally interpreted as two reading frames, fmu and fmv. The recombinant protein from E. coli was shown to methylate only C967 of small subunit (16S) ribosomal RNA and to produce only m5C at that position. The seed alignment is built from bacterial sequences only. Eukaryotic homologs include Nop2, a protein required for processing pre-rRNA, that is likely also a rRNA methyltransferase, although the fine specificity may differ. Cutoff scores are set to avoid treating archaeal and eukaroytic homologs automatically as functionally equivalent, although they may have very similar roles. [Protein synthesis, tRNA and rRNA base modification]
Jiyao W et al.(2023). "The conserved domain database in 2023.",