Articles of Significant Interest Selected from This Issue by the Editors

摘要

Next Section Analysis of a Novel Iron-Regulated Factor Required for Iron Acquisition from a Host Heme Source Corynebacterium diphtheriae requires multiple surface proteins to acquire iron from the hemoglobin-haptoglobin complex (Hb-Hp). Lyman et al. (e00676-17) identified an additional Hb-Hp binding protein, HbpA, that has a crucial role in iron acquisition from this important host hemoprotein. Localization studies show that HbpA is anchored to the cell surface and secreted into the environment, indicating that it may function in both locations to facilitate heme iron uptake from Hb-Hp. HbpA, which is found only in a subset of C. diphtheriae strains, appears to represent a new class of bacterial Hb- and Hb-Hp-binding proteins. Previous SectionNext Section Antisense Expression in the Pseudomonas fleQ Gene Opposes AlgU-Dependent Downregulation of Motility AlgU regulates 17% of Pseudomonas syringae pv. tomato DC3000 genes, including those for virulence and flagella. Markel et al. (e00576-17) determined that AlgU directly upregulates antisense expression of P. syringae fleQ, the gene encoding the master regulator of flagellar biosynthesis in Pseudomonas. While AlgU strongly reduces flagellar gene expression and motility, fleQ antisense expression increases motility without altering flagellar gene expression. The AlgU-dependent fleQ antisense promoter is conserved in most pseudomonads that also encode an AlgU ortholog, suggesting that AlgU-dependent fleQ antisense expression has important functions in most of the genus Pseudomonas. Previous Section? DNA Polymerase Sequence-Specific Binding Reveals Evolutionary/Biochemical Links with RNA Polymerases The evolutionary origin of single-subunit DNA-dependent RNA polymerase (ssRNAPs) is uncertain. Fenstermacher et al. (e00579-17) use a SELEX (systematic evolution of ligands by exponential enrichment)-based protocol to demonstrate that Taq and Klenow polymerases preferentially bind primer-template sequences that contained core promoter elements from T3 and T7 phage RNAPs. These data suggest the intriguing possibility that phage RNA polymerases exploited intrinsic binding affinities of ancestral DNA polymerases to develop promoters. Conversely, DNA polymerases could have evolved from related RNA polymerases and retained the intrinsic binding preference despite there being no clear function for such a preference in DNA biology.