Affiliation:
1. Department of Microbiology, Pusan National University, Busan, South Korea
2. Nano-Bio Electron Microscopy Research Team, Korea Basic Science Institute, Daejeon, South Korea
Abstract
ABSTRACT
In the presence of alanine, AldR, which belongs to the Lrp/AsnC family of transcriptional regulators and regulates
ald
encoding alanine dehydrogenase in
Mycobacterium smegmatis
, changes its quaternary structure from a homodimer to an octamer with an open-ring conformation. Four AldR-binding sites (O2, O1, O4, and O3) with a consensus sequence of GA/T-N
2
-NWW/WWN-N
2
-A/TC were identified upstream of the
M. smegmatis
ald
gene by means of DNase I footprinting analysis. O2, O1, and O4 are required for the induction of
ald
expression by alanine, while O3 is directly involved in the repression of
ald
expression. In addition to O3, both O1 and O4 are also necessary for full repression of
ald
expression in the absence of alanine, due to cooperative binding of AldR dimers to O1, O4, and O3. Binding of a molecule of the AldR octamer to the
ald
control region was demonstrated to require two AldR-binding sites separated by three helical turns between their centers and one additional binding site that is in phase with the two AldR-binding sites. The cooperative binding of AldR dimers to DNA requires three AldR-binding sites that are aligned with a periodicity of three helical turns. The
aldR
gene is negatively autoregulated independently of alanine. Comparative analysis of
ald
expression of
M. smegmatis
and
Mycobacterium tuberculosis
in conjunction with sequence analysis of both
ald
control regions led us to suggest that the expression of the
ald
genes in both mycobacterial species is regulated by the same mechanism.
IMPORTANCE
In mycobacteria, alanine dehydrogenase (Ald) is the enzyme required both to utilize alanine as a nitrogen source and to grow under hypoxic conditions by maintaining the redox state of the NADH/NAD
+
pool. Expression of the
ald
gene was reported to be regulated by the AldR regulator that belongs to the Lrp/AsnC (feast/famine) family, but the underlying mechanism was unknown. This study revealed the regulation mechanism of
ald
in
Mycobacterium smegmatis
and
Mycobacterium tuberculosis
. Furthermore, a generalized arrangement pattern of
cis
-acting regulatory sites for Lrp/AsnC (feast/famine) family regulators is suggested in this study.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
13 articles.
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