In Escherichia coli as many as nine different genes coding for proteins with significant homology to peptidyl-prolyl cis/trans-isomerases (PPIases) have been found. However, for three of them, the histidine-rich SlyD, the homologous gene product of ORF149, and parvulin-like SurA, it was not known whether these proteins really possess PPIase activity. To gain access to the full set of PPIases in E. coli, SlyD, the N-terminal fragment of SlyD devoid of the histidine-rich region, as well as the protein product of ORF149 of E. coli named SlpA (SlyD-like protein) were cloned, overexpressed, and purified to apparent homogeneity. On the basis of the amino acid sequences, both proteins proved to be of the FK506-binding protein type of PPIases. Only when using trypsin instead of chymotrypsin as helper enzyme in the PPIase assay, the enzymatic activity of full-length SlyD and its N-terminal fragment can be measured. For SucAla-Phe-Pro-Arg-4-nitroanilide as substrate, k cat /K m of 29,600 M ؊1 s ؊1 for SlyD and 18,600 M ؊1 s ؊1 for the Nterminal fragment were obtained. Surprisingly, the PPIase activity of SlyD is reversibly regulated by binding of three Ni 2؉ ions to the histidine-rich, C-terminal region. Because the PPIase activity of SlpA could be established as well, we now know eight distinct PPIases with proven enzyme activity in E. coli.Peptidyl-prolyl cis/trans-isomerases (PPIases, 1 EC 5.2.1.8.) are able to accelerate the cis-trans-isomerization of the Xaa-Pro peptide bond in polypeptide chains (1). They are divided into three families, the cyclophilins, FK506-binding proteins (FKBP) including the putative subfamily of trigger factors, and parvulins. Members of all three PPIase families have been found in Escherichia coli (2-6).The slyD gene (sensitivity to lysis) was identified by screening for survival of E. coli C after induction of the cloned lysis gene E of bacteriophage X174 (7). Mutations mapped to the slyD locus (at 73.5Ј on the E. coli chromosome) resulted in accumulation of complete phages inside the cells, but no lysis occurred. The slyD locus was cloned and sequenced. By deletion analysis it was demonstrated that the open reading frame 196 of E. coli is identical to slyD (8). The derived amino acid sequence of SlyD was shown to share similarity with FKBPs.

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Three-dimensional topological insulators are fascinating materials with insulating bulk yet metallic surfaces that host highly mobile charge carriers with locked spin and momentum. Remarkably, surface currents with tunable direction and magnitude can be launched with tailored light beams. To better understand the underlying mechanisms, the current dynamics need to be resolved on the timescale of elementary scattering events (∼10 fs). Here, we excite and measure photocurrents in the model topological insulator Bi2Se3 with a time resolution of 20 fs by sampling the concomitantly emitted broadband terahertz (THz) electromagnetic field from 0.3 to 40 THz. Strikingly, the surface current response is dominated by an ultrafast charge transfer along the Se–Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to be orders of magnitude smaller than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are of direct relevance for broadband optoelectronic devices based on topological-insulator surface currents.

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Avian rotaviruses are broadly distributed among birds, but only scarcely characterized on the molecular level. The VP4-, VP6-, VP7- and NSP5-encoding sequences of eight group A rotaviruses from chickens and turkeys determined here indicate a low degree of sequence similarity with mammalian rotaviruses. An NSP6-encoding region was missing in all chicken isolates except for isolate Ch2. Four novel genotypes (P[30], P[31], G22 and H8) were assigned by the Rotavirus Classification Working Group. Generally, chicken and turkey isolates clustered into separate branches of phylogenetic trees. However, chicken isolate Ch2 consistently clustered together with turkey isolates. Chicken isolate 06V0661G1 has a VP4-encoding sequence of unknown origin, but possesses VP6, VP7 and NSP5 genotypes typical for chicken isolates. These results might indicate interspecies transmission and reassortment among avian group A rotaviruses under field conditions. PCR protocols enabling amplification of avian and mammalian group A rotaviruses were developed for use in further epidemiological studies.