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The histidine residue at the 95th position (His-95) in the halorhodopsin (HR) of Halobacterium salinarium is essential for the chloride binding and pumping activity of the HR. The replacement of His-95 decreases the chloride pumping activity and formation of the intermediates of the photoreaction at low chloride levels. At physiological levels of chloride, the activity of the mutants is comparable to that of the wild-type HR. The expression and stability of the mutant HRs is less than that of the wild-type HR.

The primary structures of helices A to G of three new bacteriorhodopsin (BR)-like retinal proteins were determined. Several oligonucleotide primers at the A-, C- and G-helix parts of BR were designed, and the gene encoding the A- to G-helix region of BR-like protein were amplified by the polymerase chain reaction method. Together, the results of the sequence analysis suggest that BR and BR-like proteins can be classified into three types (halobium BR, mex BR or aR,and port BR), and each group has about 50-60 percent amino acid sequence homology.

New halobacterial strains were isolated from crude solar salts commercially produced in Mexico and Australia. The bacteriorhodopsin, halorhodopsin, sensory rhodopsin and phoborhodopsin-like pigment levels in five of the isolated strains were determined by flash spectroscopy and light-induced ion transport measurements. DNA hybridization analysis showed that the genes coding for BR and HR are not homologous to the corresponding genes in Halobacterium halobium R1.

A cDNA encoding a proline (Pro) transporter (ProT) was isolated and characterized from a cDNA library prepared from 14-d-old seedlings of Oryza sativa cv. Akibare. The deduced amino acid sequence of the rice ProT protein (OsProT) had 68.8% homology to the ProT protein 1 from Arabidopsis thaliana and 59.6% homology to that from Lycopersicon esculentum. Northern blot analysis revealed that the gene for OsProT (OsProT) was expressed in all organs examined, comparatively strongly in leaf sheath and stem. Salt treatment did not induce expression of OsProT but strongly induced expression of the gene for Δ1-pyrroline-5-carboxylate synthetase (P5CS), a key enzyme in Pro biosynthesis. Southern blot analysis revealed that OsProT has a gene family. OsProT specifically transported l-Pro in a transport assay using Xenopus laevis oocytes. [ABSTRACT FROM AUTHOR]

Abstract: P-glycoprotein (P-gp; MDR1) recognizes and actively transports many structurally diverse compounds (hydrophobic neutral and cationic). We studied MDR1-mediated drug transport using a high-throughput (96-well) oocyte expression system. MDR1-expressing oocytes contained sufficient ATP levels to conduct fundamental efflux studies; the optimal experimental temperature was 25°C. [3H]Vinblastine efflux by MDR1-expressing oocytes was detectable and afforded a K m of 145.5±25.4μM. [3H]Vinblastine (5.6±0.3μM) and [3H]digoxin (1.0±0.1μM) were individually injected into MDR1-expressing oocytes and their efflux monitored. Quinidine and verapamil, known MDR1 substrates/inhibitors, showed trans-inhibition on MDR1-mediated [3H]vinblastine and [3H]digoxin efflux. Conversely, doxorubicin demonstrated cis-inhibition without trans-inhibition on MDR1-mediated [3H]vinblastine efflux. The MDR1-expressing oocyte system offers researchers with an alternative in vitro method to screen compounds and may allow one to probe P-gp drug–drug and/or drug–inhibitor interactions. [Copyright &y& Elsevier]

Using deep sequencing (deepCAGE), the FANTOM4 study measured the genome-wide dynamics of transcription-start-site usage in the human monocytic cell line THP-1 throughout a time course of growth arrest and differentiation. Modeling the expression dynamics in terms of predicted cis-regulatory sites, we identified the key transcription regulators, their time-dependent activities and target genes. Systematic siRNA knockdown of 52 transcription factors confirmed the roles of individual factors in the regulatory network. Our results indicate that cellular states are constrained by complex networks involving both positive and negative regulatory interactions among substantial numbers of transcription factors and that no single transcription factor is both necessary and sufficient to drive the differentiation process.