Regulation of expression of type I signal peptidases in Listeria monocytogenes

Abstract

The role of type I signal peptidases (SPases I) is to remove the signal peptides of preproteins exported by the general secretory pathway. The genome of Listeria monocytogenes contains a locus encoding three contiguous SPases I (denoted SipX, SipY and SipZ). The authors recently showed that SipX and SipZ perform distinct functions in protein secretion and bacterial pathogenicity. Here, the regulation of sip gene expression in broth and in infected eukaryotic cells was studied. The results show that expression of the three sip genes is (i) controlled by two distinct promoter regions that respond differently to growth phase and temperature variations, and (ii) influenced by PrfA (the transcriptional activator regulating most of the virulence genes of L. monocytogenes) and the stress proteins ClpC and ClpP. It was found that sip gene expression was strongly upregulated upon infection of eukaryotic cells when bacteria were still entrapped in the phagosomal compartment. This upregulation is compatible with the need of L. monocytogenes to optimize its production of virulence factors in the early stage of the intracellular cycle.

The arsenal of virulence factors deployed byListeria monocytogenesto promote its cell infection cycle

“…177 Independent studies have then identified nearly 160 L. monocytogenes EGD-e genes whose expression is directly or indirectly dependent on PrfA. 92,[178][179][180][181][182] …”

lmo1273, a novel gene involved in Listeria monocytogenes virulence

“…We have shown previously that the expression of the sip locus is regulated by two different promoters, P sipX and P sipZ , producing a large transcript covering the entire locus (sipX-lmo1273) and a shorter one compatible with a transcription starting upstream of sipZ (sipZ-lmo1273) (Bonnemain et al, 2004;Raynaud & Charbit, 2005). Notably, the genomic organization and DNA sequence of the locus are highly conserved in the other sequenced Listeria genomes, including in L. innocua and in the recently sequenced genome of L. welshimeri .…”

“…We have previously identified a five-gene locus, designated sip (lmo1269-lmo1273), in the genome of L. monocytogenes EGD-e, encoding three paralogous type I signal peptidases (SPases I) (Bonnemain et al, 2004) involved in bacterial virulence. We showed that this locus was under the control of two distinct promoters, one preceding lmo1269 (designated sipX) and a second preceding lmo1271 (designated sipZ) (Raynaud & Charbit, 2005). The two distal genes of the locus (lmo1272 and lmo1273), which are co-transcribed with the SPase I genes (Raynaud & Charbit, 2005), encode proteins sharing significant similarities with the YlqF and RnhB proteins, respectively, of Bacillus subtilis.…”

“…We showed that this locus was under the control of two distinct promoters, one preceding lmo1269 (designated sipX) and a second preceding lmo1271 (designated sipZ) (Raynaud & Charbit, 2005). The two distal genes of the locus (lmo1272 and lmo1273), which are co-transcribed with the SPase I genes (Raynaud & Charbit, 2005), encode proteins sharing significant similarities with the YlqF and RnhB proteins, respectively, of Bacillus subtilis. In the latter organism, RnhB is involved in RNA-DNA heteroduplex degradation (Itaya et al, 1999;Ohtani et al, 1999a) and YlqF participates in ribosome biogenesis (Matsuo et al, 2006;Uicker et al, 2007).…”

“…The lmo1273 coding sequence (including the ribosomebinding site) was amplified from EGD-e genomic DNA by PCR using primers 22 and 24. To ensure efficient transcription, lmo1273 was cloned downstream of the P sipX promoter (Raynaud & Charbit, 2005), the main promoter of the sip locus. The P sipX region was amplified with primers 20 and 21.…”