Abstract
The molecular mechanism for regulation of the genes involved in the biosynthesis of amino acids is poorly identified in Thermus thermophilus. In this study, we analyzed the transcriptional control of the major lysine biosynthetic gene cluster in T. thermophilus. S1 nuclease mapping revealed that the transcription, which is repressed by lysine, starts at 111 bp, upstream of the translational start codon, ATG, for the homocitrate synthase (hcs) gene. The 5'-leader region of 111 bp carries a sequence that can encode a short peptide of 14 amino acids with tandem-arranged lysine residues in its sequence. The nucleotide sequence of the region suggests that the transcript can form complicated secondary structures. Deletion of most of the 5'-leader region or mutation of the tandem lysine codons suppressed the transcriptional repression by lysine. Mutation of the tandem codons from lysine to glutamine resulted in glutamine-dependent repression of the gene connected downstream, indicating that the leader peptide mediated the transcriptional attenuation of the gene expression. This is the first report demonstrating the transcriptional regulation of amino acid biosynthesis in T. thermophilus.
Highlights
Two pathways are known for lysine biosynthesis: the diaminopimelate pathway found in most bacteria and plants, and the ␣-aminoadipate (AAA)1 pathway found in yeast and fungi [1]
A DNA fragment was amplified for the connecting portion between every two genes when the samples were treated with reverse transcriptase. This suggested that all genes in the cluster form an operon, which is transcribed in a polycistronic manner, and the expression of genes involved in lysine AAA biosynthesis is controlled by the promoter located in the upstream region of the hcs gene
We examined the effect of other amino acids, glutamate, alanine, arginine, and threonine, on ␣-galactosidase expression in T. thermophilus harboring pTthcs[K2/Q2]-plp, and we found that the addition of these amino acids did not decrease ␣-galactosidase expression, and the only exception was obtained with glutamate
Summary
Two pathways are known for lysine biosynthesis: the diaminopimelate pathway found in most bacteria and plants, and the ␣-aminoadipate (AAA) pathway found in yeast and fungi [1]. The results indicate that gene expression is regulated through a mechanism similar to that known for the trp operon in Escherichia coli [10, 11]. This is the first report demonstrating the regulatory mechanism of expression of genes involved in amino acid biosynthesis in T. thermophilus
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