An unusual bacterial reverse transcriptase having LVDD in the YXDD box from Escherichia coli

A minor population of wild strains of Escherichia coli contains a gene for reverse transcriptase (RT) which is responsible for the synthesis of multicopy single-stranded DNA (msDNA), a branched DNA-RNA complex. A DNA fragment capable of synthesizing msDNA was cloned from strain ECOR-58, one of the 72 wild strains in the ECOR collection. The complete open reading frame of a novel reverse transcriptase, designated ECOR-58 RT, was identified. ECOR-58 RT consisted of 408 amino acid residues, and its 227-residue polymerase domain from residue 43 to 269 showed significant homologies to all the other bacterial RTs so far identified. Most significantly, its YXDD box, the most highly conserved sequence in all RTs from prokaryotes to eukaryotes, was found to be replaced with LVDD. ECOR-58 RT was found to be most distantly related in a phylogenetic tree to all 9 other bacterial RTs so far identified.