Mutational inactivation of both
nonA and
nonB genes are required for the permissiveness of
Bacillus subtilis Marburg cells to infection by phage SP10. By transformational analysis of the
nonA strain with DNAs from gently lysed protoplasts carrying the integrative plasmid pMUTIN (
em) insertions in every 20 kb along the whole chromosome, we have identified the
nonA to be the cured state of endogenous prophage SPβ. Direct DNA sequencing, on the other hand, revealed one nonsense mutation of
nonB in
ydiR, which is a component gene of the intrinsic restriction system
BsuMR of
B.subtilis Marburg. Introduction of the wild type
ydiR into the
nonB strain at
aprE locus resulted in complementation of
nonB. Furthermore, as the SP10 genome was found to possess multiple
BsuM target sites, it is considered that SP10 can infect and multiply in
B.subtilis cells, which are SPβ free and possess a defective
BsuMR restriction system.
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