Inhibitory effects of endothelin-1 and endothelin-3 on prolactin release: possible involvement of endogenous endothelin isopeptides in the rat anterior pituitary.

Spontaneous prolactin release from the isolated rat anterior pituitary was inhibited by endothelin-1 in a dose-dependent manner (10(-8)-10(-6) M). Endothelin-3 also inhibited spontaneous prolactin release with an almost identical dose-response relationship as endothelin-1. These inhibitory effects were unaffected by application of a dopamine D2-receptor antagonist, YM-09151-2 (10(-7) M). Rat anterior and posterior pituitary glands were abundant in both endothelin-1 and endothelin-3, as compared with other regions of the brain. The present results suggest that endogenous endothelin-1 and endothelin-3 in the anterior and posterior pituitary are involved in the inhibitory regulation of prolactin secretion as autocrine or paracrine factors.     

Comparative analyses of human immunodeficiency virus type 1 (HIV-1) and HIV-2 Vif mutants.

Virion infectivity factor (vif), a gene found in all lentiviruses, plays an essential role in virus replication in certain target cells. We examined the replication competence of the human immunodeficiency virus type 2 (HIV-2) vif mutant in different T-cell lines and primary cells in comparison with that of the HIV-1 vif mutant. Both mutant viruses were unable to replicate in peripheral blood-derived mononuclear cells but replicated with wild-type efficiency in certain T-cell lines, such as SupT1 and MOLT-4/8. These results confirm the importance of vif in the infection of relevant target cells and imply that some cellular factor(s) could compensate for vif function. However, HIV-1 and HIV-2 vif mutant viruses also show differential replications in other cell lines, suggesting either different threshold requirements for the same cellular factor(s) or the involvement of different factors to compensate for vif-1 and vif-2 functions. By cross complementation experiments, we showed that vif-1 and vif-2 have similar functions. Our studies further indicate the existence of two kinds of nonpermissive cells: H9 is unable to complement HIV-1 delta vif but is susceptible to a one-round infection with HIV-1 delta vif produced from permissive cells. In contrast, U937 is nonpermissive for HIV-2 delta vif produced from permissive cells but, once infected, is able to complement the delta vif function. In both types of nonpermissive cells, a step prior to proviral DNA synthesis is affected.     

Cloning,characterization and overproduction of nuclease S1 gene (nucS) from Aspergillus oryzae

The nuclease S1 gene (nucS) from Aspergillus oryzae was isolated using a polymerase-chain-reaction-amplified DNA fragment as a probe, and a 2.6-kb SalI-EcoRI fragment containing the nucS gene was sequenced. It was deduced that the nucS gene had two short introns, 49 and 50 nucleotides in lenght. The nucS gene had an open-reading frame of 963 base pairs and coded for a protein of 287 amino acid residues, comprising the signal peptide of 20 amino acids and a mature protein of 267 amino acids. The deduced amino acid sequence agreed well with the published amino acid sequence except for one substitution. Southern hybridization analysis showed that the nucS gene existed as a single copy in the A. oryzae chromosome. When the structural gene of nucS was fused with the promoter of the glaA gene and introduced into A. oryzae, the yield od secreted nuclease S1 increased about 100-fold compared with the recipient strain.     

Lipase modulator protein (LimL) of Pseudomonas sp. strain 109.

Plasmids containing a Pseudomonas sp. strain 109 extracellular lipase gene (lipL) lacking NH2-terminal sequence and a lipase modulator gene (limL) lacking the NH2-terminal hydrophobic region were constructed and expressed independently in Escherichia coli by using the T7 promoter expression vector system. Recombinant LipL (rLipL) was produced as inclusion bodies, whereas recombinant LimL (rLimL) was present as a soluble protein. During in vitro renaturation of the purified rLipL inclusion bodies after they had been dissolved in 8 M urea, addition of rLimL was essential to solubilize and modulate rLipL. The solubility and activity of rLipL were influenced by the rLimL/rLipL molar ratio; the highest level of solubility was obtained at an rLimL/rLipL ratio of 4:5, whereas the highest activity level was obtained at an rLimL/rLipL ratio of 4:1. After renaturation, rLipL and rLimL were coprecipitated with anti-rLipL antibody, indicating the formation of an rLipL-rLimL complex. Activity of the native lipase purified from Pseudomonas sp. strain 109 was also inhibited by rLimL. By Western blotting (immunoblotting) with anti-rLimL antibody, native LimL was detected in Pseudomonas cells solubilized by sarcosyl treatment. LimL was purified from Pseudomonas sp. strain 109, and the NH2-terminal amino acid sequence was determined to be NH2-Leu-Glu-Pro-Ser-Pro-Ala-Pro-. We propose that to prevent membrane degradation, LimL weakens lipase activity inside the cell, especially in the periplasm, in addition to modulating lipase folding.     

Factors necessary for the export process of colicin E1 across cytoplasmic membrane of Escherichia coli

Factors necessary for the export process of colicin E1 across the cytoplasmic membrane of Escherichia coli were investigated. beta-Galactosidase activities from gene fusions between the colicin E1 and lacZ genes were recovered in the inner membrane fraction of E. coli when the region containing the internal signal-like sequence of colicin E1 [M. Yamada et al. (1982) Proc. Natl Acad. Sci. USA 79, 2827-2831] was present, but were found in the soluble fraction when the region was eliminated. The colicin E1 export was reduced upon insertion mutation in a gene that is located downstream from the colicin E1 gene in the same operon and responsible for mitomycin-C-induced killing of the host cell. A frame shift mutation of the colicin E1 plasmid was constructed to direct the protein which had lost the COOH-terminal 13 residues of original colicin E1 and was altered in 6 residues of the new COOH-terminal portion. The aberrant colicin E1 that was inducibly synthesized remained inside the cells. These results indicate that colicin E1 is exported with the aid of a product of the downstream gene and that the COOH-terminal portion is necessary for the export. The binding of colicin E1 to the cytoplasmic membrane through the internal signal-like sequence may be a step in the protein export process.