Plasmid-derived llad II restriction-modification system from lactococcus lactis

摘要

A number of type II restriction-modification (R-M) systems have been derived from plasmids found in Lactococcus lactis strains from the Danish starter culture TK5. The R-M systems LlaAI, LlaBI and LlaDII are claimed with their nucleotide sequences containing open reading frames (ORFs) coding for restriction endonucleases and corresponding methylases. Also a DNA cassette comprising one or more of the R-M systems and fragments thereof in combination with DNA encoding other phage resistance mechanisms is claimed as are cloning and expression vectors including DNA selected from the group consisting of the R-M systems, fragments thereof and DNA cassette, cells transformed with the expression vectors, a method of conferring increased virus resistance on a cell, and the individual restriction endonucleases and methylases of the R-M systems.