RESTRICTION-MODIFICATION SYSTEMS IN THE MARINE, AEROBIC, NITROGEN-FIXING UNICELLULAR CYANOBACTERIUM CYANOTHECE SP. ATCC-51142

Cyanothece sp. ATCC 51142 possesses six host restriction-modification systems (HRMS), and these HRMS were designated as Csp68KI to Csp68KVI. So far, four restriction enzymes have been characterized biochemicall y, and the other two were deduced based on the cloning of correspondin g DNA methyltransferase genes M, Csp68KIV and M. Csp68KV from the Cyan othece genome. Csp68KI, Csp68KII, Csp68KIII, Csp68KIV, Csp68KV, and Cs p68KVI are isoschizomers of Avail, AsuII, AvaIII, MspI, HaeIII, and Fn uDII, respectively. The cleavage specificities for Csp68KI, Csp68KII, Csp68KIII, and Csp68KVI were characterized. The Cyanothece restriction enzymes showed different temperature and salt requirements for their optimal activity. For example, the restriction enzyme Csp68KII functio ns optimally at 50 degrees C and Csp68KIII requires higher salt for it s activity.