Comprised of two aptamers connected by a short nucleotide linker, the glycine riboswitch was the first example of naturally occurring RNA elements reported to bind small organic molecules cooperatively. Earlier works have shown binding of glycine to the second aptamer allows tertiary interactions to be made between the two aptamers, which facilitates binding of a separate glycine molecule to the first aptamer, leading to glycine-binding cooperativity. Prompted by a distinctive protection pattern in the linker region of a minimal glycine riboswitch construct, we have identified a highly conserved (>90%) leader-linker duplex involving leader nucleotides upstream of the previously reported consensus glycine riboswitch sequences. In >50% of the glycine riboswitches, the leader-linker interaction forms a kink-turn motif. Characterization of three glycine ribsowitches showed that the leader-linker interaction improved the glycine-binding affinities by 4.5-to 86-fold. In-line probing and native gel assays with two aptamers in trans suggested synergistic action between glycine-binding and interaptamer interaction during global folding of the glycine riboswitch. Mutational analysis showed that there appeared to be no ligand-binding cooperativity in the glycine riboswitch when the leader-linker interaction is present, and the previously measured cooperativity is simply an artifact of a truncated construct missing the leader sequence.

Hansen's disease (leprosy) is an ancient condition characterized by hypopigmented patches that progress to become plaques with hypoesthesia. Several case reports suggest that armadillos may be a source of Mycobacterium leprae for clinical cases, and contact with armadillos has been shown to be a significant risk factor in several case-control studies. Early diagnosis and treatment result in an excellent prognosis and provide an effective means to prevent complications of peripheral nerve injury, social stigma, and disability. We present a case of Hansen's disease in a previously healthy veteran and provide an overview of the diagnosis, classification, and treatment of the condition. Clinicians should consider leprosy in the differential diagnosis when confronted with chronic skin lesions in the appropriate clinical setting.

Glycine riboswitches contain two aptamers and turn on the expression of downstream genes in bacteria. Although full-length glycine riboswitches were shown to exhibit no glycine-binding cooperativity, the truncated glycine riboswitches were confirmed to bind two glycine molecules cooperatively. Thorough understanding of the ligand-binding cooperativity may shed light on the molecular basis of the cooperativity and help design novel intricate biosensing genetic circuits for application in synthetic biology. A previously proposed sequential model does not readily provide explanation for published data showing a deleterious mutation in the first aptamer inhibiting the glycine binding of the second one. Using the glycine riboswitch from Vibrio cholerae as a model system, we have identified a region in the first aptamer that modulates the second aptamer function especially in the shortened glycine riboswitch. Importantly, this modulation can be rescued by the addition of a complementary oligodeoxynucleotide, demonstrating the feasibility of developing this system into novel genetic circuits that sense both glycine and a DNA signal.

The purpose of this study is to examine the incidence of aortic dissection and pseudo‐aortic dissection (dissection that has occurred as a result of the embalming process) in the gross anatomy lab. Eighty cadaveric specimens from two separate schools of medicine were screened for aortic dissection. Institution A received anatomical donations that had been initially embalmed by funeral services and embalmed a second time by the institution's director of anatomical facilities (N=31). Anatomical specimens screened at Institution B were subjected to a single embalming process at the institutional site (N=49). The incidence of suspected dissections from Institution A was 9.7%. The incidence of suspected dissections from Institution B was 6.1%. The cadavers suspected of incidence had their aortae removed and sectioned for gross and/or microscopic examination (N=3 from Institution A; N=3 from Institution B). Routine H&E preparations were used to confirm true aortic dissection after gross examination. Tissue changes that occur, as part of the embalming process, are important to identify when using aortic specimens for both teaching and research purposes. Results indicate that pseudo‐aortic dissections may occur during the embalming process and, consequently, resemble pathological disease.Grant Funding Source: none