Regulation of Excision of Integrative and Potentially Conjugative Elements from <i>Streptococcus thermophilus</i>: Role of the <i>arp1</i> Repressor

Abstract

The integrative and conjugative elements (ICEs) excise by site-specific recombination between <i>attL</i> and <i>attR</i> flanking sites, self-transfer the resulting circular form and integrate into the genome of the recipient cell. Two putative ICEs, ICE<i>St1</i> and ICE<i>St3</i>, are integrated in the same locus in 2 strains of <i>Streptococcus</i><i>thermophilus</i>. ICE<i>St1</i> is a composite element harbouring an internal recombination site, <i>attL’</i>. The recombination between <i>attL’</i> and <i>attR</i> leads to the excision of a shorter putative ICE, ICE<i>St2</i>. ICE<i>St1</i>/ICE<i>St2</i> and ICE<i>St3</i> carry related regulation modules sharing the open reading frame <i>arp1</i> that encodes a protein related to the cI repressor of the phage λ. 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<i>St1</i>, ICE<i>St2 </i>and ICE<i>St3</i>. Furthermore, the <i>arp1</i> deletion leads to a 1,000-fold increase in the excision of ICE<i>St1</i> and ICE<i>St2</i> and to a decrease in the excision induction by mitomycin C. Thus, all together, these results suggest that the autocleavage of the <i>arp1</i> repressor is involved in derepression of the <i>S</i>. <i>thermophilus</i> putative ICE excision by mitomycin C.