Active repression by thyroid hormone receptor splicing variant alpha2 requires specific regulatory elements in the context of native triiodothyronine-regulated gene promoters.

Structural requirements for the inhibitory action of thyroid hormone receptor splicing variant alpha2 (TR alpha2) on T3/TRbeta1-mediated transactivation were investigated in native promoters of two T3-regulated genes: the brain-specific myelin basic protein (MBP) and the housekeeping malic enzyme (ME). T3/TRbeta1 transactivation of MBP256-chloramphenicol acetyl transferase (CAT) and ME315-CAT constructs was inhibited and unaffected by TR alpha2, respectively. In electrophoretic mobility shift assays, TR alpha2 bound MBP-thyroid response element (TRE) as a monomer but failed to interact with ME-TRE.

Differential 9-cis-retinoic acid-dependent transcriptional activation by murine retinoid X receptor alpha (RXR alpha) and RXR beta. Role of cell type and RXR domains.

The 9-cis-retinoic acid (9cRA)-inducible enhancer of the rat cellular retinol-binding protein type II gene (CRBP II) was shown to be differentially regulated by the murine retinoid X receptor alpha (RXR alpha) as compared with RXR beta. Transient transfection assays performed in NIH 3T3 fibroblast cells demonstrated that RXR alpha yielded a high level of 9cRA-dependent transcription of a reporter gene linked to the CRBP II enhancer, when compared with RXR beta. This effect was cell type-dependent, since both receptors elicited comparable transcriptional activation of the same reporter in P19 embryonal carcinoma cells.

Heterodimerization of thyroid hormone (TH) receptor with H-2RIIBP (RXR beta) enhances DNA binding and TH-dependent transcriptional activation.

Steroid/TH receptors mediate transcriptional induction of promoters containing hormone response elements (HREs) through an unclear mechanism that involves receptor binding to both hormone and a HRE. Here we demonstrate that both HRE binding and the transcriptional inducing activities of one member of this family, TH receptor, were markedly enhanced by heterodimerization with H-2RIIBP, a non-TH-binding member of the steroid hormone receptor superfamily. H-2RIIBP, the mouse homologue of human retinoic acid-related receptor, was shown to form stable heterodimers with the TH receptor either in solution or when bound to a TH response element.

Thermodynamics of reversible monomer-dimer association of tubulin.

The equilibrium between the rat brain tubulin alpha beta dimer and the dissociated alpha and beta monomers has been studied by analytical ultracentrifugation with use of a new method employing short solution columns, allowing rapid equilibration and hence short runs, minimizing tubulin decay. Simultaneous analysis of the equilibrium concentration distributions of three different initial concentrations of tubulin provides clear evidence of a single equilibrium characterized by an association constant, Ka, of 4.9 X 10(6) M-1 (Kd = 2 X 10(-7) M) at 5 degrees, corresponding to a standard free energy change on association delta G degrees = -8.

Easily assembled digital data acquisition system for the analytical ultracentrifuge.

A system for the acquisition of digital data from the analytical ultracentrifuge which uses a commercially available data acquisition board, a standard IBM compatible personal computer (PC), and an interface circuit has been developed. The system uses the signal from the standard Beckman scanner. Preliminary analysis and data reduction are performed at the PC within minutes of data acquisition using simple commercially available software, and final data fitting is performed with a mainframe computer.