RT Journal Article SR Electronic(1) A1 Mellies, Jay L. A1 Larabee, Fredrick J. A1 Zarr, Melissa A. A1 Horback, Katy L. A1 Lorenzen, Emily A1 Mavor, DavidYR 2008 T1 Ler interdomain linker is essential for anti-silencing activity in enteropathogenic Escherichia coli JF Microbiology, VO 154 IS 12 SP 3624 OP 3638 DO https://doi.org/10.1099/mic.0.2008/023382-0 PB Microbiology Society, SN 1465-2080, AB Enteropathogenic Escherichia coli (EPEC) expresses a type III secretion system (T3SS) required for pathogenesis. Regulation of the genes encoding the T3SS is complex; two major regulators control transcription, the silencer H-NS, and the related H-NS-like protein Ler. Our laboratory is interested in understanding the molecular differences that distinguish the anti-silencer Ler from H-NS, and how Ler differentially regulates EPEC virulence genes. Here, we demonstrate that mutated Ler proteins either containing H-NS α-helices 1 and 2, missing from Ler, or truncated for the 11 aa C-terminal extension compared with the related H-NS protein, did not appreciably alter Ler function. In contrast, mutating the proline at position 92 of Ler, in the conserved C-terminal DNA binding motif, eliminated Ler activity. Inserting 11 H-NS-specific amino acids, 11 alanines or 6 alanines into the Ler linker severely impaired the ability of Ler to increase LEE5 transcription. To extend our analysis, we constructed six chimeric proteins containing the N terminus, linker region or C terminus of Ler in different combinations with the complementary domains of H-NS, and monitored their in vivo activities. Replacing the Ler linker domain with that of H-NS, or replacing the Ler C-terminal, DNA binding domain with that of H-NS eliminated the ability of Ler to increase transcription at the LEE5 promoter. Thus, the linker and C-terminal domains of Ler and H-NS are not functionally equivalent. Conversely, replacing the H-NS linker region with that of Ler caused increased transcription at LEE5 in a strain deleted for hns. In summary, the interdomain linker specific to Ler is necessary for anti-silencing activity in EPEC., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.2008/023382-0