An unusual gene containing a dnaJ N-terminal box flanks the putative origin of replication of Mycoplasma genitalium.

Origins of replication are known to be highly conserved among widely divergent microbial species, with the gene order in those regions being dnaA-dnaN-recF-gyrB. On the basis of sequence identities to entries in GenBank, the gene order of a 6-kb fragment of Mycoplasma genitalium DNA was determined to be dnaN-orf311-gyrB-gyrA-serS, which is structurally similar to the ancestral origin of replication. We have directly linked the dnaN gene to the M. genitalium dnaA gene by PCR amplification. However, we found a novel open reading frame, designated orf311, in place of an expected sequence encoding recF. Orf311 contains a DnaJ box motif at its N terminus, but it has no overall homology to any other protein or sequence in the database. We are unable to detect any recF homolog in M. genitalium by hybridization or during a random sequencing survey of the genome.