Identification of the first eubacterial endonuclease coded by an intein allele in the pps1 gene of mycobacteria

A survey of a vast range of mycobacterial strains led us to discover a new Pps1 intein allele in Mycobacterium gastri which differs from those of Myco bacterium tuberculosis and Mycobacterium leprae in both its sequence and in sertion site. While little is known about Pps1, except that it belongs to t he YC24 family of ABC transporters, we show that, unlike the other inteins described so far from Eubacteria, the MgaPps1 intein possesses a specific e ndonuclease activity. The intein is the first eubacterial intein to be char acterised as an endonuclease. Like other intein endonucleases, its minimal sequence for recognition and cleavage is quite large, with 22 bp spanning t he Pps1-c site. The fact that an active endonuclease is found among the myc obacterial inteins supports the concept of a cyclical model of invasion by horizontal transfer of these genes, followed by degeneration and loss until a new invasion event, thus explaining their long-term persistence in close ly related eubacterial species.