This domain is found in Ribosomal RNA small subunit methyltransferase F from Escherichia coli (YebU) and similar proteins mainly from proteobacteria. YebU requires S-adenosyl-l-methionine (SAM) to specifically methylate the cytosine at position 1407 of assembled 30 S rRNA subunits. This proteins is organized into two distinct structural domains: the N-terminal MTase domain (catalytic domain), which can be divided in Pfam:PF17125 and Pfam:PF01189, and the C-terminal, also consisting of two subdomains. This entry represents the first of these subdomains, which is found N-terminal to the PUA- like domain (Pfam:PF13636). The pre-PUA domain has six beta-strands that form a central sheet in an anti-parallel fashion, and three alpha-helices packing against the edges of the sheet [1].

1: The structure of the RNA m5C methyltransferase YebU from Escherichia coli reveals a C-terminal RNA-recruiting PUA domain. Hallberg BM, Ericsson UB, Johnson KA, Andersen NM, Douthwaite S, Nordlund P, Beuscher AE 4th, Erlandsen H; J Mol Biol. 2006;360:774-787. PMID:16793063