A 3.9 kb DNA fragment containing the dnaA gene region of Mycobacterium avium was cloned and its nucleotide sequence was determined. Nucleotide sequence analyses indicated that this region encodes three genes in the order rpmH (ribosomal protein L34), dnaA (the putative initiator protein) and dnaN (the β subunit of DNA polymerase III). The intergenic regions between the rpmH-dnaA and dnaA-dnaN genes were found to contain several putative DnaA boxes, 9 nt long DnaA protein recognition sequences. A DNA fragment containing the 3' but not the 5' flanking region of the M. avium dnaA gene when cloned in Escherichia coli plasmids, which are otherwise non-replicative in mycobacteria, exhibited autonomous replication activity in M. avium but not in Mycobacterium bovis BCG and Mycobacterium smegmatis. The 5' flanking region of dnaA, on the other hand, exhibited autonomous replication activity in M. bovis BCG but not in M. avium and M. smegmatis. The implications of these results for the understanding of the M. avium oriC replication initiation process are discussed.
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