SpoU protein ofEscherichia colibelongs to a new family of putative rRNA methylases

SpoU is encoded by the fourth open reading frame (ORF) of the spo operon of Escherichia coli (1). The 5'-terminal gene of this operon, gmk, encodes guanylate kinase; the second gene, rpoZ, encodes the w subunit of RNA polymerase; the third gene, spoT, encodes ppGpp hydrolase, and the 3'-terminal gene, recG, encodes a helicase-like protein involved in recombination (1 and references therein). SpoU is the only functionally uncharacterized ORF in the spo operon. Comparison of the amino acid sequence of SpoU with amino acid and nucleotide sequence databases using the programs BLASTP and TBLASTN (2), respectively, revealed high similarity to an unannotated ORF from Rhodospirillum rubrum