Sequence comparison of the chromosomal regions encompassing the internalin C genes (inlC ) of Listeria monocytogenes and L. ivanovii

Abstract

We have recently cloned and characterized the inlC gene of Listeria monocytogenes which belongs to the listerial internalin multigene family and codes for a 30-kDa secreted protein containing five consecutive leucine-rich repeats. Here, we show that in L. monocytogenes inlC is located between the rplS gene (encoding the 50S ribosomal protein L19), and the infC gene (encoding the translation initiation factor 3). By direct and inverse polymerase chain reactions (PCR), we cloned a 5.4-kb region containing a homologous gene (termed i-inlC) from L. ivanovii, the other pathogenic member of the genus Listeria. In this microorganism, the i-inlC gene is preceded by another internalin gene, i-inlD, which seems to be specific for L. ivanovii, as this gene could not be detected in L. monocytogenes by Southern hybridization with an i-inlD gene probe. The i-inlD gene also encodes a small secretory internalin (i-InlD), which shares extended homology with (i-)InlC. Upstream of i-inlD are genes for 23S rRNA and 5S rRNA, and two tRNA genes [Asn-tDNA (GTT) and Thr-tDNA(GGT)]. The 3′ terminus of the Thr-tRNA gene appears to be the site of an insertion of a genetic element including i-inlC and i-inlD. A putative transcriptional regulator gene, the product of which contains the TetR family signature, is located downstream of i-inlC. This chromosomal arrangement and the difference in chromosomal position of the two inlC genes on their respective chromosomes may be due to horizontal transfer of this gene. Transcription of i-inlC and i-inlD is strictly dependent on the transcriptional activator PrfA, which regulates transcription of most of the known virulence genes (including inlC) of L. monocytogenes and of L. ivanovii.