LdrP, a cAMP receptor protein/FNR family transcriptional regulator, serves as a positive regulator for the light-inducible gene cluster in the megaplasmid of Thermus thermophilus

Abstract

LdrP (TT_P0055) (LitR-dependent regulatory protein) is one of the four cAMP receptor protein (CRP)/FNR family transcriptional regulators retained by the extremely thermophilic bacterium Thermus thermophilus. Previously, we reported that LdrP served as a positive regulator for the light-induced transcription of crtB, a carotenoid biosynthesis gene encoded on the megaplasmid of this organism. Here, we showed that LdrP also functions as an activator of the expression of genes clustered around the crtB gene under the control of LitR, an adenosyl B12-bound light-sensitive regulator. Transcriptome analysis revealed the existence of 19 LitR-dependent genes on the megaplasmid. S1 nuclease protection assay confirmed that the promoters preceding TT_P0044 (P44), TT_P0049 (P49) and TT_P0070 (P70) were activated upon illumination in the WT strain. An ldrP mutant lost the ability to activate P44, P49 and P70, whilst disruption of litR resulted in constitutive transcription from these promoters irrespective of illumination, indicating that these genes were photo-dependently regulated by LdrP and LitR. An in vitro transcription experiment demonstrated that LdrP directly activated mRNA synthesis from P44 and P70 by the Thermus RNA polymerase holocomplex. The present evidence indicated that LdrP was the positive regulator essential for the transcription of the T. thermophilus light-inducible cluster encoded on the megaplasmid.

Role and Function of LitR, an Adenosyl B 12 -Bound Light-Sensitive Regulator of Bacillus megaterium QM B1551, in Regulation of Carotenoid Production

“…he LitR (light-induced transcription regulator)/CarH family is a MerR family of transcriptional regulatory proteins that contain a cobalamin (Cbl; synonym, vitamin B 12 )-binding domain at the C terminus (1)(2)(3)(4). The first observation regarding the involvement of vitamin B 12 in the light-inducible carotenoid (Crt) production of the Gram-negative gliding bacterium Myxococcus xanthus was presented by Cervantes and Murillo (5).…”

“…In vivo and in vitro studies showed that LitR directly binds to the intergenic promoter region of litR and crtB to repress bidirectional transcription under dark conditions. Light irradiation causes the inactivation of LitR, which in turn allows the expression of LdrP, directly activating the transcription of the crt biosynthesis gene cluster and the genes adjacent to litR (2). Interestingly, litR, cobalamin biosynthe-sis, and other light-inducible genes, including the crt genes, were all found to be located on the large plasmid of this organism (2).…”

New light on vitamin B12: The adenosylcobalamin-dependent photoreceptor protein CarH

“…19 The photoreceptor proteins were first discovered in the bacterium Myxococcus xanthus, 6,[18][19][20] which turns red in the presence of light, as a result of the synthesis of carotenoids, but is pale yellow in the dark. However, carotenoids have also been found in a variety of other bacteria, including Streptomyces coelicolor [21][22][23] , Thermus thermophilus [24][25][26] and Bacillus megaterium 27 . Homologous sequences to the photoreceptor protein are found in the genomes of many bacteria and these proteins are probably widely distributed in non-photosynthetic bacteria.…”

“…Homologous sequences to the photoreceptor protein are found in the genomes of many bacteria and these proteins are probably widely distributed in non-photosynthetic bacteria. 6,17,19,22,25,26 The photoreceptor proteins were named CarH in M. xanthus 20 , TtCarH 25 or LitR 24 in T. thermophilus and LitR 27 in B. megaterium, but, for simplicity, and because the photoreceptor proteins are all very similar, in this review I shall use the designation CarH for the protein and carH for the gene.…”

“…6,[18][19][20][21][22][23][24][25][26][27] These bacteria produce carotenoids -yellow, orange or red pigments -which protect them from photo-oxidative damage by quenching the singlet oxygen free radicals produced by absorption of energy from light. 19 The photoreceptor proteins were first discovered in the bacterium Myxococcus xanthus, 6,[18][19][20] which turns red in the presence of light, as a result of the synthesis of carotenoids, but is pale yellow in the dark.…”