A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1

Insects utilize xenobiotic compounds to up-and downregulate cytochrome P450 monooxygenases(P450s)involved in detoxification of toxic xenobiotics including phytochemicals and pesticides.G-quadruplexes(G4)-forming DNA motifs are enriched in the promoter regions of transcription factors and function as cis-acting elements to regulate these genes.Whether and how P450s gain and keep G4 DNA motifs to regulate their expression still remain unexplored.Here,we show that CYP321A1,a xenobiotic-metabolizing P450 from Helicoverpa zea,a polyphagous insect of economic importance,has acquired and preserved a G4 DNA motif by selectively retaining a transposon known as HzIS1-3 that carries this G4 DNA motif in its promoter region.The HzIS1-3 G4 DNA motif acts as a silencer to suppress the constitutive and induced expression of CYP321A1 by plant allelochemicals flavone and xanthotoxin through folding into an intramolecular parallel or hybrid-1 conformation in the absence or presence of K^(+).The G4 ligand N-methylmesoporphyrin IX(NMM)strengthens the silencing effect of HzIS1-3 G4 DNA motif by switching its structure from hybrid-1 to hybrid-2.The enrichment of transposons in P450s and other environment-adaptation genes implies that selective retention of G4 DNA motif-carrying transposons may be the main evolutionary route for these genes to obtain G4 DNA motifs.

Novel mitochondrial 16S rRNA mutation, 3200T→C, associated with adult-onset type 2 diabetes

Objective To investigate the role of a potential diabetes related mitochondrial region, which includes two previously reported mutations, 3243AG and 3316GA, in Chinese patients with adult onset type 2 diabetes Methods A total of 277 patients and 241 normal subjects were recruited for the study Mitochondrial nt 3116-3353, which spans the 16S rRNA, tRNA leu(UUR) and the NADH dehydrogenase 1 gene, were detected using polymerase chain reaction (PCR), direct DNA sequencing, PCR restriction fragment length polymorphism and allele specific PCR Variants were analyzed by two tailed Fisher exact test The function of the variants in 16S rRNA were predicted for minimal free energy secondary structures by RNA folding software mfold version 3 Results Four homoplasmic nucleotide substitutions were observed, 3200TC, 3206CT, 3290TC and 3316GA Only the 3200TC mutation is present in the diabetic population and absent in the control population No statistically significant associations were found between the other three variants and type 2 diabetes The 3200TC and 3206CT nucleotide substitutions located in 16S rRNA are novel variants The 3200TC caused a great alteration in the minimal free energy secondary structure model while the 3206CT altered normal 16S rRNA structure little Conclusions The results suggest that the 3200TC mutation is linked to the development of type 2 diabetes, but that the other observed mutations are neutral In contrast to the Japanese studies, the 3316GA does not appear to be related to type 2 diabetes