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The human RNA editing enzyme ADAR1 (double-stranded RNA deaminase I) deaminates adenine in pre-mRNA to yield inosine, which codes as guanine. ADAR1 has two left-handed Z-DNA binding domains, Z alpha and Z beta, at its NH(2)-terminus and preferentially binds Z-DNA, rather than B-DNA, with high binding affinity. The cocrystal structure of Z alpha(ADAR1) complexed to Z-DNA showed that one monomeric Z alpha(ADAR1) domain binds to one strand of double-stranded DNA and a second Z alpha(ADAR1) monomer binds to the opposite strand with 2-fold symmetry with respect to DNA helical axis. It remains unclear how Z alpha(ADAR1) protein specifically recognizes Z-DNA sequence in a sea of B-DNA to produce the stable Z alpha(ADAR1)-Z-DNA complex during the B-Z transition induced by Z alpha(ADAR1). In order to characterize the molecular recognition of Z-DNA by Z alpha(ADAR1), we performed circular dichroism (CD) and NMR experiments with complexes of Zalpha(ADAR1) bound to d(CGCGCG)(2) (referred to as CG6) produced at a variety of protein-to-DNA molar ratios. From this study, we identified the intermediate states of the CG6-Z alpha(ADAR1) complex and calculated their relative populations as a function of the Z alpha(ADAR1) concentration. These findings support an active B-Z transition mechanism in which the Z alpha(ADAR1) protein first binds to B-DNA and then converts it to left-handed Z-DNA, a conformation that is then stabilized by the additional binding of a second Z alpha(ADAR1) molecule.

No abstract

The genus Fritillaria belongs to the widely distributed Liliaceae. The bulbs of Fritillaria, F. ussuriensis and F. cirrhosa are valuable herbaceous medicinal ingredients. However, they are still used indiscriminately in herbal medicine. Identification and molecular phylogenic analysis of Fritillaria species are therefore required. Here, we report the complete chloroplast (CP) genome sequences of F. ussuriensis and F. cirrhosa. The two Fritillaria CP genomes were 151,524 and 151,083 bp in length, respectively, and each included a pair of inverted repeated regions (52,678 and 52,156 bp) that was separated by a large single copy region (81,732 and 81,390 bp), and a small single copy region (17,114 and 17,537 bp). A total of 111 genes in F. ussuriensis and 112 in F. cirrhosa comprised 77 protein-coding regions in F. ussuriensis and 78 in F. cirrhosa, 30 transfer RNA (tRNA) genes, and four ribosomal RNA (rRNA) genes. The gene order, content, and orientation of the two Fritillaria CP genomes exhibited the general structure of flowering plants, and were similar to those of other Fritillaria species. Comparison of the six Fritillaria species’ CP genomes indicated seven highly divergent regions in intergenic spacers and in the matK, rpoC1, rpoC2, ycf1, ycf2, ndhD, and ndhF coding regions. We established the position of the six species through phylogenic analysis. The complete chloroplast genome sequences of the two Fritillaria species and a comparison study are useful genomic information for identifying and for studying the phylogenetic relationship among Fritillaria species within the Liliaceae.