Oligomerization and DNA binding of Ler, a master regulator of pathogenicity of enterohemorrhagic and enteropathogenic Escherichia coli

Ler is a DNA-binding, oligomerizable protein that regulates pathogenicity islands in enterohemorrhagic and enteropathogenic Escherichia coli strains. Ler counteracts the transcriptional silencing effect of H-NS, another oligomerizable nucleoid-associated protein. We studied the oligomerization of Ler in the absence and presence of DNA by atomic force microscopy. Ler forms compact particles with a multimodal size distribution corresponding to multiples of 35 units of Ler. DNA wraps around Ler particles that contain more than 1516 Ler monomers. The resulting shortening of the DNA contour length is in agreement with previous measurements of the length of DNA protected by Ler in footprinting assays. We propose that the repetition unit corresponds to the number of monomers per turn of a tight helical Ler oligomer. While the repressor (H-NS) and anti-repressor (Ler) have similar DNA-binding domains, their oligomerization domains are unrelated. We suggest that the different oligomerization behavior of the two proteins explains the opposite results of their interaction with the same or proximal regions of DNA.

Hybrid turbo FEC/ARQ systems and distributed space-time coding for cooperative transmission

Cooperative transmission can be seen as a "virtual" MIMO system, where themultiple transmit antennas are in fact implemented distributed by the antennas both at the source and the relay terminal. Depending on the system design, diversity/multiplexing gainsare achievable. This design involves the definition of the type of retransmission (incrementalredundancy, repetition coding), the design of the distributed space-time codes, the errorcorrecting scheme, the operation of the relay (decode&forward or amplify&forward) and thenumber of antennas at each terminal. Proposed schemes are evaluated in different conditionsin combination with forward error correcting codes (FEC), both for linear and near-optimum(sphere decoder) receivers, for its possible implementation in downlink high speed packetservices of cellular networks. Results show the benefits of coded cooperation over directtransmission in terms of increased throughput. It is shown that multiplexing gains areobserved even if the mobile station features a single antenna, provided that cell wide reuse of the relay radio resource is possible.

Morphological priming in Spanish verb forms: an ERP repetition priming study

The ERP repetition priming paradigm has been shown to be sensitive to the processing differences between regular and irregular verb forms in English and German. The purpose of the present study is to extend this research to a language with a different inflectional system, Spanish. The design (delayed visual repetition priming) was adopted from our previous study on English, and the specific linguistic phenomena we examined are priming relations between different kinds of stem (or root) forms. There were two experimental conditions: In the first condition, the prime and the target shared the same stem form, e.g., "ando-andar" [I walk-to walk], whereas in the second condition, the prime contained a marked (alternated) stem, e.g., "duermo-dormir" [I sleep-to sleep]. A reduced N400 was found for unmarked (nonalternated) stems in the primed condition, whereas marked stems showed no such effect. Moreover, control conditions demonstrated that the surface form properties (i.e., the different degree of phonetic and orthographic overlap between primes and targets) do not explain the observed priming difference. The ERP priming effect for verb forms with unmarked stems in Spanish is parallel to that found for regularly inflected verb forms in English and German. We argue that effective priming is possible because prime target pairs such as "ando-andar" access the same lexical entry for their stems. By contrast, verb forms with alternated stems (e.g., "duermo") constitute separate lexical entries, and are therefore less powerful primes for their corresponding base forms.