Regulation of excision of integrative and potentially conjugative elements from streptococcus thermophilus: Role of the arp1 repressor

The integrative and conjugative elements (ICEs) excise by site-specific recombination between attL and attR flanking sites, self-transfer the resulting circular form and integrate into the genome of the recipient cell. Two putative ICEs, ICESt1 and ICESt3, are integrated in the same locus in 2 strains of Streptococcus thermophilus. ICESt1 is a composite element harbouring an internal recombination site, attL'. The recombination between attL' and attR leads to the excision of a shorter putative ICE, ICESt2. ICE St1/ICESt2 and ICESt3 carry related regulation modules sharing the open reading frame arp1 that encodes a protein related to the cl repressor of the phage gimel. The repressors belonging to this family autoproteolyse in the presence of damaged DNA. Treatments with mitomycin C induce an increase in the excision of ICE St1, ICESt2 and ICESt3. Furthermore, the arp1 deletion leads to a 1,000 fold increase in the excision of ICE St1 and ICESt2 and to a decrease in the excision induction by mitomycin C. Thus, all together, these results suggest that the autocleavage of the arp1 repressor is involved in derepression of the S. thermophilus putative ICE excision by mitomycin C. Copyright (c) 2008 S. Karger AG, Basel.