BceS1, a new addition to the type III restriction and modification family

The nucleotide sequence of an 11-kb chromosomal Bg/II fragment from Bacillu s cereus American Type Culture Collection (ATCC) 10987 strain revealed two closely adjacent open reading frames organized in an operon, of which the d educed amino acids showed identity to the type III restriction and modifica tion (R/M) subunits described in Gram-negative bacteria. An enhanced transc ription level was revealed when the culture was grown in the presence of fo reign DNA. A cell-free extract from this culture restricted pUC19, whereas from a plain medium the restriction was very weak. The in vitro methylation protected pUC 19 from restriction. The R/M system was designated BceS1 as this endonuclease required ATP and Mg2+ as cofactors like other type III en donucleases. BceS1 is the first chromosomal type III R/M system characteriz ed in a Gram-positive bacterium. (C) 2001 Federation of European Microbiolo gical Societies. Published by Elsevier Science B.V. All rights reserved.