Coupling DNA-binding and ATP hydrolysis in Escherichia coli RecQ: role of a highly conserved aromatic-rich sequence

RecQ enzymes are broadly conserved Superfamily-2 (SF-2) DNA helicases that play critical roles in DNA metabolism. RecQ proteins use the energy of ATP hydrolysis to drive DNA unwinding; however, the mechanisms by which RecQ links ATPase activity to DNA-binding/unwinding are unknown. In many Superfamily-1 (SF-1) DNA helicases, helicase sequence motif III links these activities by binding both single-stranded (ss) DNA and ATP. However, the ssDNA-binding aromatic-rich element in motif III present in these enzymes is missing from SF-2 helicases, raising the question of how these enzymes link ATP hydrolysis to DNA-binding/unwinding. We show that Escherichia coli RecQ contains a conserved aromatic-rich loop in its helicase domain between motifs II and III. Although placement of the RecQ aromatic-rich loop is topologically distinct relative to the SF-1 enzymes, both loops map to similar tertiary structural positions. We examined the functions of the E.coli RecQ aromatic-rich loop using RecQ variants with single amino acid substitutions within the segment. Our results indicate that the aromatic-rich loop in RecQ is critical for coupling ATPase and DNA-binding/unwinding activities. Our studies also suggest that RecQ's aromatic-rich loop might couple ATP hydrolysis to DNA-binding in a mechanistically distinct manner from SF-1 helicases

Im Zwielicht. Schatten-Dialoge bei Andersen, Fechner und Nietzsche

Nietzsche's dialogue "The Wanderer and His Shadow", which frames his book of the same name, is examined for its intertextual references to other texts in which the motif of the shadow plays a central role: On Hans-Christian Andersen's fairy tale "The Shadow" and Gustav Theodor Fechner's "The Shadow is Alive".Nietzsches Dialog "Der Wanderer und sein Schatten", das sein gleichnamiges Buch rahmt, wird auf seine intertextuellen Bezüge zu anderen Texten, in denen das Motiv des Schatten eine zentrale Rolle spielt, untersucht: Auf Hans-Christian Andersens Märchen "Der Schatten" und Gustav Theodor Fechners "Der Schatten ist lebendig"