Bacillus subtilis encodes a discrete flap endonuclease that cleaves RNA-DNA hybrids.

The current model for Okazaki fragment maturation in bacteria invokes RNA cleavage by RNase H, followed by strand displacement synthesis and 5' RNA flap removal by DNA polymerase I (Pol I). RNA removal by Pol I is thought to occur through the 5'-3' flap endo/exonuclease (FEN) domain, located in the N-terminus of the protein. In addition to Pol I, many bacteria encode a second, Pol I-independent FEN.