This protein family includes YcaO and homologs that can phosphorylate a peptide amide backbone (rather than side chains), as during heterocycle-forming modifications during maturation of the TOMM class (Thiazole/Oxazole-Modified Microcins) of bacteriocins. However, YcaO domain proteins also occur in contexts that do not suggest peptide modification. [Hypothetical proteins, Conserved]
Jiyao W et al.(2023). "The conserved domain database in 2023.",