Febs Letters

doi: 10.1016/0014-5793(91)80001-Jpmid: N/A

Mesnard, Jean-Michel; Lebeurier, Geneviéve

doi: 10.1016/0014-5793(91)80002-Kpmid: 1715279

Reverse transcription is not solely a retroviral mechanism. Hepadnaviruses and caulimoviruses have RNA intermediates that are reverse transcribed into DNA. Moreover non‐viral retroelements, retrotransposons, use reverse transcription in their transposition. All these retroelements encode reverse transcriptase but each group developed their own expression modes capable of assuring a specific and efficient replication of their genomes.

Ikeuchi, Masahiko; Nyhus, Karin J.; Inoue, Yorinao; Pakrasi, Himadri B.

doi: 10.1016/0014-5793(91)80003-Lpmid: 1908790

Photosystem I (PSI) complex of Anabaena variabilis ATCC 29413 consists of at least 11 subunits, 9 of which are resolved by high resolution gel electrophoresis. N‐terminal amino acid sequences of the four subunits with molecular masses of 6.8, 5.2, 4.8 and 3.5 kDa were determined. Based on the sequence homology, the 3.5 kDa subunit was revealed to correspond to PSI‐I (the gene product of psaI), which had so far been detected only in higher plant PSI complexes. The 6.8 kDa protein and 4.8 kDa protein were identified as gene products of psaK and psaJ, respectively. The 5.2 kDa protein was homologous to a 4.8 kDa subunit of PSI of the thermophilic cyanobacterium Synechococcus vulcanus, suggesting that this protein is a component of PSI in cyanobacteria.

Desideri, A.; Stefanini, S.; Polizio, F.; Petruzzelli, R.; Chiancone, E.

doi: 10.1016/0014-5793(91)80004-Mpmid: 1715280

Apoferritin has been selectively labeled with a maleimide nitroxide derivative at Cys‐126, located in the hydrophilic 3‐fold channels. Titration of this derivative with Fe(II), which gives rise to the initial Fe(III)‐apoferritin complex, produces, at low metal‐to‐protein ratios, a decrease of the intensity of the label EPR signal due to the occurrence of a magnetic dipolar interaction. A label‐metal distance ranging between 8–12 Å can be estimated from titrations performed with VO(IV), which is known to bind in the 3‐fold channels, and likewise produces a decrease in the label EPR signal. The present findings indicate that iron binds in the hydrophilic channels in its higher oxidation slate and that these channels represent the metal entry route at least at low metal‐to‐protein ratios.

Fujimoto, Ichiro; Ikenaka, Kazuhiro; Kondo, Tetsuro; Aimoto, Saburo; Kuno, Miyuki; Mikoshiba, Katsuhiko

doi: 10.1016/0014-5793(91)80005-Npmid: 1908786

The MCD peptide in bee venom induces degranulation in mast cells. The internal calcium concentration of mast cells increased and remained high following MCD stimulation. This calcium increase was blocked by pertussis toxin (Ptx) treatment, suggesting that MCD peptide activates Ptx‐sensitive G‐protein. Even in the absence of external calcium in the incubation medium, the calcium concentration increased by MCD treatment. but soon returned to the original level. D‐MCD, the optical isomer of the MCD peptide, also increased the internal calcium concentration through a Ptx‐sensitive pathway. We suggest that cationic clusters at one side of the surface are more important in activating the G‐protein than the α‐helix conformation.

Galkina, S.I.; Ivanov, V.V.; Preobrazhensky, S.N.; Margolis, L.B.; Bergelson, L.D.

doi: 10.1016/0014-5793(91)80006-Opmid: 1879530

Under physiological conditions significant amounts of low‐density lipoprotein LDL particles ar taken up by cells independently of specific high affinity LDL receptors (apo‐B receptors). Previously it was established that some cells contain surface sites capable of binding liposomes. We proposed that liposome‐binding sites could contribute to LDL interaction with the cell surface via phospholipid molecules of LDL particles. To check this hypothesis we studied the competitive interaction of human LDL and DPPC liposomes with mouse embryo fibroblasts depleted of apo‐B receptors by preliminary incubation with LDL. We have found that after removal of the liposome‐binding sites from cell lamellae these areas of the cell surface lose their ability to bind LDL.

Hosoda, Kiminori; Nakao, Kazuwa; Hiroshi-Arai, ; Suga, Shin-ichi; Ogawa, Yoshihiro; Mukoyama, Masashi; Shirakami, Gotaro; Saito, Yoshihiko; Nakanishi, Shigetada; Imura, Hiroo

doi: 10.1016/0014-5793(91)80007-Ppmid: 1652463

We isolated a human endothelin‐1 (ET‐1) receptor cDNA from a human placenta cDNA library. The cDNA encodes a 427‐amino acid protein with seven putative transmembrane domains. The rank order of the binding to the receptor expressed in COS‐7 cells was: ET‐1 ⩾ ET‐2 ⪢ ET‐3. The receptor expressed in Xenopus oocytes showed a potent electrophysiological response to 1 × 10−7 M ET‐1 under voltage clamp at −60 mV, while a much weaker response was produced by 1 × 10−7 M ET‐3. Northern blot analysis with RNA from human tissues revealed a single band with a size of 4.3 kb in a wide variety of human tissues, especially highly in the blood vessel.

Buchstaller, A.; Adamiker, D.; Fuchs, K.; Sieghart, W.

doi: 10.1016/0014-5793(91)80008-Qpmid: 1715287

β2‐ and β3‐subunits of GABAA receptors purified from the brains of 5–10‐day‐old rats were investigated in the intact or completely N‐deglycosylated state using the β‐subunit‐specific monoclonal antibody bd‐17 and polyclonal antibodies directed against synthetic amino acid sequences specific for the GABAA receptor β2‐ or β3‐subunits. The present results seem to indicate the existence of two different isoforms of the β3‐subunit and several different isoforms of the β2‐subunit of the GABAA receptor which probably are produced by alternative splicing.

Didžiapetris, Remigijus; Drabnig, Barbara; Schellenberger, Volker; Jakubke, Hans-Dieter; S̆vedas, Vytas

doi: 10.1016/0014-5793(91)80009-Rpmid: 1879533

Penicillin acylase from E. coli is able to catalyze both the introduction and the removal of the phenylacetyl group. We have established that phenylacetyl derivatives of amino acids and peptides can be used in protease‐catalyzed peptide synthesis. Here the synthesis of leucine‐enkephalin using enzymes for N‐terminal amino group protection, peptide bond formation and deprotection is described.

Kamps, Jan A.A.M.; Kuiper, Johan; Kar Kruijt, J.; van Berkel, Theo J.C.

doi: 10.1016/0014-5793(91)80010-Zpmid: 1879534

The effect of LDL and β‐VLDL on the expression of the LDL receptor is studied in cultured human parenchymal cells. The high affinity binding of [125I]LDL to cultured human parenchymal cells was down regulated to 37.3±2.9% and 24.0±2.6% of the control value, after preincubation with LDL or β‐VLDL for 22 h, respectively. When LDL receptor synthesis was blocked at 22 h a residual receptor activity of 29% is noticed, indicating a half‐life of LDL receptors in human parenchymal cells of 12 h. It is concluded that LDL receptor expression on human liver parenchymal cells is subject to complete down‐regulation by β‐VLDL, which may be held responsible for the cholesterol‐rich diet induced down‐regulation of LDL receptors, in vivo.