DAX-1 (dosage-sensitive sex reversal-adrenal hypoplasia congenita-critical region on the X chromosome gene 1; NR0B1) is an orphan nuclear receptor that plays an important role in the development and functioning of the adrenal gland and hypothalamic-pituitary gonadal axis. The DAX-1 protein acts as a transcriptional repressor of genes involved in the steroidogenic pathway. We have identified a novel isoform encoded by the known exon 1 of DAX-1 and a previously unrecognized exon (exon 2alpha) that lies within intron 1 of DAX-1. This novel transcript, which we designated DAX-1alpha, is terminated at exon 2alpha; the last 70 amino acids of the C-terminal repressor domain encoded by exon 2 are absent. DAX-1alpha encodes a protein of 401 amino acids; the first 389 amino acids are encoded by exon 1 and the last 12 are encoded by exon 2alpha. Using conventional RT-PCR and real-time RT-PCR analyses, we found that DAX-1alpha is abundantly expressed in the adrenal gland, brain, kidney, ovary, and testis. We also found that DAX-1alpha can bind to steroidogenic factor 1 and to DNA but is unable to repress steroidogenic factor 1-mediated transcriptional activation of the reporter gene and acts as an antagonist of DAX-1 under certain conditions.
Sucrose synthase (SUS) plays an important
role in carbohydrate
metabolism in plants. The SUS genes in licorice remain unknown. To
reveal the sucrose metabolic pathway in licorice, all the 12 putative
SUS genes of Glycyrrhiza uralensis were
systematically identified by genome mining, and two novel SUSs (GuSUS1
and GuSUS2) were isolated and characterized for the first time. Furthermore,
we found that the flexible N-terminus was responsible for the low
stability of plant SUSs, and deletion of redundant N-terminus improved
the stability of GuSUS1 and GuSUS2. The half-life of both GuSUS1 and
GuSUS2 mutants was increased by 2-fold. Finally, the GuSUS1 mutant
was coupled with UGT73C11 for the glycosylation of glycyrrhetinic
acid (GA) with uridine 5′-diphosphate disodium salt hydrate
(UDP) in situ recycling, and GA conversion was increased
by 7-fold. Our study not only identified the SUS genes in licorice
but also provided a stable SUS mutant for the construction of an efficient
UDP-recycling system for GA glycosylation.
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