The type III machinery of Yersinia transports Yop proteins across the bacterial envelope. The minimal secretion signal of yopQ is located in codons 1-10 that, when fused in frame to the neomycin phosphotransferase gene, is sufficient to promote type III secretion of YopQ1-10-Npt. Frame-shift mutations, generated by nucleotide insertions or deletions following the AUG start and suppressed at the fusion site with npt, abrogate signalling of yopQ1-10 but not of yopQ1-15. By generating transversions of every single nucleotide in yopQ1-10, we identified 10 nucleotide positions in codons 2, 3, 5, 7, 9 and 10 that were each required for substrate recognition. One transversion that abolishes secretion, uridyl 9 to adenyl (U9A), is a synonymous codon 3 mutation that retains the original amino acid as confirmed by Edman degradation analysis, suggesting that the mRNA but not the amino acid sequence of yopQ1-10 is involved in secretion signalling. Although transversion of U8A abrogates signalling of yopQ 1-10, fusion of yopQ codons 11-15 restores secretion. The nucleotides that are required for this suppression by yopQ11-15 were identified and revealed both synonymous and non-synonymous mutations. Frame-shift mutations introduced into just this suppressor region (codons 11-15) did not abrogate its ability to suppress mutations in the minimal secretion signal (codons 1-10). Thus, elements downstream of the minimal secretion signal of YopQ increase the efficiency of YopQ secretion and suppress mutations elsewhere in the secretion signal.
CITATION STYLE
Ramamurthi, K. S., & Schneewind, O. (2003). Yersinia yopQ mRNa encodes a bipartite type III secretion signal in the first 15 codons. Molecular Microbiology, 50(4), 1189–1198. https://doi.org/10.1046/j.1365-2958.2003.03772.x
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