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TNAs [(L)-alpha-threofuranosyl oligonucleotides] containing vicinally connected (3'-->2') phosphodiester bridges undergo informational base pairing in antiparallel strand orientation and are capable of cross-pairing with RNA and DNA. Being derived from a sugar containing only four carbons, TNA is structurally the simplest of all potentially natural oligonucleotide-type nucleic acid alternatives studied thus far. This, along with the base-pairing properties of TNA, warrants close scrutiny of the system in the context of the problem of RNA's origin.

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The crystal structures of the human androgen receptor (hAR) and human progesterone receptor ligandbinding domains in complex with the same ligand metribolone (R1881) have been determined. Both threedimensional structures show the typical nuclear receptor fold. The change of two residues in the ligandbinding pocket between the human progesterone receptor and hAR is most likely the source for the specificity of R1881 to the hAR. The structural implications of the 14 known mutations in the ligand-binding pocket of the hAR ligand-binding domains associated with either prostate cancer or the partial or complete androgen receptor insensitivity syndrome were analyzed. The effects of most of these mutants could be explained on the basis of the crystal structure. Androgen (AR)1 and progesterone receptors (PR) are members of the superfamily of nuclear receptors that includes the steroid receptors, among others, as well as the vitamin D, thyroid, retinoic acid receptors, and the so-called orphan receptors. In addition, AR and PR are members of a group of four closely related steroid receptors including the mineralocorticoid receptor and the glucocorticoid receptor recognizing the same hormone response element. In general, steroid receptors are comprised of five to six domains and act as ligand-activated transcription factors that control the expression of specific genes. To date, no experimentally determined three-dimensional structure is available for a complete receptor. During the past few years, x-ray structures have been published for two of the domains, the DNA-binding domain as well as for a number of ligand-binding domains (LBD) including LBD⅐ligand complexes of the estrogen receptor ␣ and ␤, the PR, the vitamin D receptor, the retinoic acid receptors (X,RXR; acid, RAR), the thyroid hormone receptor, and the peroxisome proliferatoractivated receptors (1-13). Despite the low sequence homology of as low as 20% between the LBDs of different nuclear receptor families, all these proteins share a similar fold. They are comprised of up to 12 helices and a small ␤-sheet arranged in a so-called ␣-helical sandwich, a kind of fold that up to now has only been observed for the LBDs of nuclear receptors. Depending on the nature of the bound ligand, agonist, or antagonist, the carboxyl-terminal helix H12 is found in either one of two orientations. In the agonist-bound conformation, helix H12 serves as a "lid" to close the ligand-binding pocket (LBP), whereas in the antagonist-bound conformation helix H12 is positioned in a different orientation thus opening the entrance to the LBP.Androgens and their receptors play an important role in male physiology and pathology.

Diabetes mellitus is an important risk factor for mortality and morbidity among those undergoing CABG. Research is needed to determine if good control of glucose levels during the perioperative time period improves outcome.