Identification of a protein encoded by the trans activator gene tatIII of human T-cell lymphotropic retrovirus type III.

The human T-cell lymphotropic virus type III (HTLV-III/LAV) is a retrovirus associated with acquired immune deficiency syndrome. The region on the viral genome that is necessary for trans-activation of the HTLV-III/LAV long terminal repeat called tatIII has previously been determined to lie between nucleotides 5365 and 5607. Here we report that a bacterial fusion protein containing amino acid sequences specified by the first coding exon of the tatIII gene is recognized by some patient antisera. We also demonstrate that lymphoid and epithelial cells that express the trans activator function express a 14-kilodalton (kDa) protein recognized by a patient antiserum that reacts with the bacterial tatIII fusion protein. Cells transiently transfected with a deletion mutant of the trans activator protein produce a 12-kDa protein rather than the 14-kDa protein. These observations indicate that the tatIII region contains a functional gene and is capable of expressing a protein that migrates with an apparent molecular size of 14 kDa in some lymphoid and epithelial cells transfected with plasmids containing the tatIII region. We propose that the product of the trans activator gene be designated p14tat-III.     

Hormonal regulation of the development of protease and carboxypeptidase activities in barley aleurone layers

Carboxypeptidase and protease activities of hormone-treated barley (Hordeum vulgare cv Himalaya) aleurone layers were investigated using the substrates N-carbobenzoxy-Ala-Phe and hemoglobin. A differential effect of gibberellic acid (GA₃) on these activities was observed. The carboxypeptidase activity develops in the aleurone layers during imbibition without the addition of hormone, while the release of this enzyme to the incubation medium is enhanced by GA₃. In contrast, GA₃ is required for both the production of protease activity in the aleurone layer and its secretion. The time course for development of protease activity in response to GA₃ is similar to that observed for α-amylase. Treating aleurone layers with both GA₃ and abscisic acid prevents all the GA₃ effects described above. Carboxypeptidase activity is maximal between pH 5 and 6, and is inhibited by diisopropylfluorophosphate and p-hydroxymercuribenzoate. We have observed three protease activities against hemoglobin which differ in charge but are all 37 kilodaltons in size on sodium dodecyl sulfate polyacrylamide gels. The activity of the proteases can be inhibited by sulfhydryl protease inhibitors, such as bromate and leupeptin, yet is enhanced by 2-fold with 2-mercaptoethanol. In addition, these enzymes appear to be active against the wheat and barley storage proteins, gliadin and hordein, respectively. On the basis of these characteristics and the time course of GA₃ response, it is concluded that the proteases represent the GA₃-induced, de novo synthesized proteases that are mainly responsible for the degradation of endosperm storage proteins.     

Barley aleurone layers secrete a nuclease in response to gibberellic Acid : purification and partial characterization of the associated ribonuclease, deoxyribonuclease, and 3'-nucleotidase activities

Incubation of barley (Hordeum vulgare L. cv Himalaya) half-seeds with gibberellic acid enhances the secretion of ribonuclease and deoxyribonuclease from aleurone tissue (MJ Chrispeels, JE Varner 1967 Plant Physiol 42: 398-406; L Taiz, JE Starks 1977 Plant Physiol 60: 182-189). These activities were over 50-fold greater in medium of half-seeds incubated with gibberellic acid than in control medium. Ribonuclease and deoxyribonuclease activities initially appeared in the medium 24 to 48 hours after hormone induction and increased for up to 96 hours. Both activities had a pH optimum of 6.0 and a temperature optimum of 55°C. When the medium from gibberellic acid-treated half-seeds was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, the major ribonuclease and deoxyribonuclease activity bands comigrated. The two enzyme activities remained associated throughout a 2,700-fold purification employing ammonium sulfate fractionation, Heparin-Agarose affinity chromatography, and Reactive Blue 2-Agarose affinity chromatography. Also accompanying the ribonuclease and deoxyribonuclease activities throughout purification was the ability to hydrolyze the 3′-phosphoester linkage of 3′-AMP. The purified protein was composed of a single polypeptide with an apparent molecular weight of 36 kilodaltons as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It is concluded that in response to gibberellic acid, barley aleurone tissue secretes a nuclease having ribonuclease, deoxyribonuclease, and 3′-nucleotidase activities.     

Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus.

A novel penicillin-binding protein, PBP-2' (Mr about 75,000), is known to be induced in excessively large amount by most beta-lactam compounds in cells of a clinically isolated strain of Staphylococcus aureus, TK784, that is highly resistant to beta-lactams and also most other antibiotics. This protein has very low affinities to most beta-lactam compounds and has been supposed to be the cause of the resistance of the cells to beta-lactams. A 14-kilobase DNA fragment was isolated from the cells that carried the gene encoding this penicillin-binding protein and also a genetically linked marker that is responsible for the resistance to tobramycin. This DNA was cloned on plasmid pACYC184 and was shown to cause both production of PBP-2' and resistance to tobramycin in Escherichia coli cells. However, the formation of PBP-2' in E. coli was only moderate and was independent of normal inducer beta-lactams. The PBP-2' formed in the E. coli cells showed slow kinetics of binding to beta-lactams similar to that of PBP-2' formed in the original S. aureus cells and gave a similar pattern of peptides to the latter when digested with the proteolytic V8 enzyme of S. aureus.     

Characterization of a DNA repair domain containing the dihydrofolate reductase gene in Chinese hamster ovary cells

The formation and removal of UV-induced pyrimidine dimers were measured in restriction fragments near and within the essential dihydrofolate reductase (DHFR) gene in Chinese hamster ovary cells in order to map the genomic fine structure of DNA repair. Dimer frequencies were determined at 0, 8, and 24 h after irradiating the cells with 20 J/m2 UV light (254 nm). Within 8 h, the cells had removed more than 40% of the dimers from sequences near the 5' end of the gene, somewhat fewer from the 3' end, but only 2% from the 3' flanking region and 10% from a region upstream from the gene. The corresponding extent of repair in the genome as a whole is 5-10% in the 8-h period. Isoschizomeric restriction enzyme analysis was used to detect the level of methylation in the fragments in which repair was measured. We found that the only hypomethylated sites in and around the DHFR gene were in the fragment near its 5' end, which displayed maximal DNA repair efficiency. The size of the region of preferential DNA repair at the DHFR locus appears to be in the range of 50-80 kilobases, and this finding is discussed in relation to genomic domains and the structure of mammalian chromatin.     

互花米草、狐米草和大绳草茎秆的比较解剖观察

互花米草、狐米草和大绳草的表皮均由长细胞、短细胞(栓质细胞和硅质细胞)、盐腺和气孔器组成。它们成纵行交互排列。盐腺的结构与大米草相似,但三个种的盐腺和气孔器的数目不同,尤其以大绳草最多。它们的内部结构是由气道、不同大小的维管束、基本组织以及厚壁组织组成。然而,维管束的数目及厚壁组织的发育各不相同。狐米草和大绳草有高度木质化的厚壁组织细胞,而互花米草的厚壁组织木质化较弱。大绳草的维管束多于其他两种。     

Variations in ADP-ribosylation of nuclear scaffold proteins during the HeLa cell cycle

Cell cycle variations in ADP-ribosylation of nuclear scaffold proteins were determined. Nuclei of synchronized cells were isolated and labeled with [32P]NAD before nuclear scaffolds were obtained by digestion of DNA with DNase I and extraction of proteins with 2M NaCl. Autoradiograms revealed the three groups of "lamins" and a species identified as poly (ADP-ribose) polymerase to be the primary ADP-ribosylated proteins. The patterns of modification of nuclear scaffold proteins displayed similar features through the cell cycle. Radioactivity in the lamins increased from 20% in early-S phase to 40% in G1 phase of the next cell cycle.     

Cellulolytic Activity of Clostridium acetobutylicum

Clostridium acetobutylicum NRRL B527 and ATCC 824 exhibited extracellular and cell-bound endoglucanase and cellobiase activities during growth in a chemically defined medium with cellobiose as the sole source of carbohydrate. For both strains, the endoglucanase was found to be mainly extracellular (70 to 90%) during growth in continuous or batch cultures with the pH maintained at 5.2, whereas the cellobiase was mainly cell associated (60 to 90%). During continuous cultivation of strain B527 with cellobiose as the limiting nutrient, maximum production of the endoglucanase and cellobiase occurred at pH values of 5.2 and 4.8, respectively. In the carbon-limited continuous cultures, strain 824 produced similar levels of endoglucanase, cellobiosidase, and cellobiase activities regardless of the carbon source used. However, in ammonium- or phosphate-limited cultures, with an excess of glucose, only 1/10 of the endoglucanase was produced, and neither cellobiosidase nor cellobiase activities were detectable. A crude extracellular enzyme preparation from strain B527 hydrolyzed carboxymethylcellulose and phosphoric acid-swollen cellulose readily and microcrystalline cellulose (A vicel) to a lesser extent. Glucose accounted for more than 90% of the reducing sugar produced by the hydrolysis of acid-swollen cellulose and Avicel. Strain B527 did not grow in medium with acid-swollen cellulose as the sole source of carbohydrate, although it grew readily on the products obtained by hydrolyzing the cellulose in vitro with a preparation of extracellular cellulase derived from the same organism.     

Proton NMR of aequorin. Structural changes concomitant with calcium-independent light emission

Aequorin, a Ca(II)-sensitive bioluminescent protein from jellyfish, emits light at 469 nm from an excited state of a substituted pyrazine (oxyluciferin) which results from the oxidation of a chromophore molecule that is noncovalently bound to the protein. The chromophore is oxidized when Ca(II) or other activating metal ions are bound by aequorin. In the absence of Ca(II), spontaneous emission of light, referred to as Ca(II)-independent light emission, occurs at a rate less than 10(-6) of that for Ca(II)-induced emission. Proton nuclear magnetic resonance (NMR), circular dichroism (CD), and fluorescence were used to study structural changes of aequorin accompanying Ca(II)-independent light emission. Time course studies by 1H NMR and CD demonstrate that as a result of Ca(II)-independent light emission, aequorin progressively changes from a rigid, fully active form showing little segmental mobility to a practically unfolded, discharged (i.e., inactive) form in which a number of amino acid residues are significantly mobile. This slow discharged protein (SDP) is distinct in nature and conformation from aequorin which has been discharged by Ca(II), i.e., the blue fluorescent protein. The rate of Ca(II)-independent discharge of aequorin is substantially reduced in the presence of excess Mg(II); the time constant for inactivation at 5 degrees C is 30 days with no Mg(II) present and 70 days with Mg(II) present. The NMR spectra are nearly identical at a given stage of inactivation whether or not Mg(II) is present. Oxyluciferin remains bound to SDP. If it is removed, however, by column chromatography, the resulting apo-SDP partially refolds, and the segmental mobility acquired in the formation of SDP is significantly attenuated particularly for some of the aromatic amino acid residues.