Molecular and serological relationships of Spartina mottle virus (SpMV) strains from Spartina spec. and from Cynodon dactylon to other members of the Potyviridae.

Spartina mottle virus (SpMV) was first reported 1980 and classified by physical and biological properties as a tentative member of the genus Rymovirus in the Potyviridae. This genus was recently separated into two genera: Rymovirus and Tritimovirus. Now the sequence of the 3'-terminal part of the genome of SpMV was determined. Additionally a virus isolate originating from Cynodon dactylon in Italy was cloned and sequenced. This Assisi-isolate shared 87.5% amino acid sequence identity with SpMV. The high degree of identity and their close serological relationship indicate that SpMV and Assisi-isolate have to be regarded as different strains of one virus. The Assisi-isolate should be designated as SpMV-AV. Comparing the C-terminal part of the ORF of several Potyviridae the sequences of SpMV strains were more similar to those of the genera Rymovirus and Potyvirus than to the genera Tritimovirus, Macluravirus, Bymovirus and Ipomovirus. The comparisons revealed identities of less than 32% for the CP and 37% for the 3'-NIb/CP region, indicating that SpMV can not be classified to any of the established genera. The results of serological tests support a separate position of SpMV in the Potyviridae. We propose to introduce the name Sparmovirus for the new genus.

Soil-borne rye mosaic and European wheat mosaic virus: two names for a furovirus with variable genome properties which is widely distributed in several cereal crops in Europe.

PCR and nucleotide sequence analyses have revealed that Soil-borne rye mosaic furovirus (SBRMV) which we have recently described is widely distributed in Europe. In Northern Germany, Poland and Denmark the virus affects mainly rye and triticale, but in France and Italy it is wheat which becomes infected. The partial RNA 1 and RNA 2 sequences which were determined for the various SBRMV sources form several clusters, but so far no correlation between molecular differences and the type of host which becomes infected under natural conditions was detected. European wheat mosaic furovirus which was recently described by Diao et al. (1999) [Virology 261: 331-339] is closely related to a French source of SBRMV.

Molecular characterization of a new furovirus mainly infecting rye.

The complete or almost complete nucleotide sequences were determined for the two RNAs of three different sources of a new furovirus which mainly infects rye and for which the name Soil-borne rye mosaic furovirus (SBRMV) is proposed. The genome organization of this virus is virtually identical to that of Soil-borne wheat mosaic furovirus (SBWMV). However, SBRMV and SBWMV differ considerably in the nucleotide sequences of their genomes and in the derived amino acid sequences of their putative gene products. The sequences of the three sources of SBRMV (two from rye and one from wheat) differ between each other in various parts of their genomes by 1% to 10%. Larger differences were found in the readthrough part of the coat protein readthrough protein. There are no indications that the relationship of the C source from wheat to the other two sources from rye is more distant than the relationship between the two sources from rye. The 3'UTRs of both SBRMV RNAs are remarkable in having a predicted upstream pseudoknot domain (UPD) with seven pseudoknots. The same number was also predicted for the UPD of SBWMV RNA 1 whereas the much shorter UDP of SBWMV RNA 2 may form only four pseudoknots.

First Report of Soilborne Rye Mosaic Virus in Rye in Denmark.

Soilborne wheat mosaic furovirus (SBWMV)-like particles were detected in rye (Secale cereale) grown in sandy soil in West Zealand during spring 1999. Infected plants showed yellow leaf mosaic and light stunting. Electron microscopy of negatively stained crude sap preparations revealed rigid rod-shaped particles with two average lengths, 296 and 162 nm; average diameter was 23 nm. Sap-inoculation to Chenopodium quinoa and C. amaranticolor produced local leaf lesions when grown at 17°C but none when grown at 22 to 25°C. All the features agree with the description of SBWMV (1). Immunosorbent electronmicroscopy with polyclonal antiserum produced by W. Huth to furovirus-like particles isolated from rye in Germany gave a distinct decoration to particles. Light microscopy of roots cleared with 10% KOH and stained with a 0.5% solution of trypan blue in lactoglycerol revealed resting spores with a morphology and size similar to Polymyxa graminis, a furovirus vector. This is the first record of a furovirus on cereals in Denmark. The complete nucleotide sequence of the isolate was analyzed and compared with data on isolates from wheat. Sequence identity was only 74%. Therefore, the isolate was designated as soilborne rye mosaic virus. SBRMV has been recorded previously in rye and triticale in several regions of Germany (2). References: (1) M. K. Brakke. 1971. CMI/AAB Descr. Plant Viruses No. 77. (2) W. Huth. Nachrichtenbl. Dtsch. Pflanzenschutzdienstes 50:163, 1998.

Immunochemical detection of CoA-modified mitochondrial matrix proteins.

An in vitro assay mixture consisting of mitochondrial matrix proteins from rat liver and CoA resulted in the formation of CoA-modified proteins. CoA-modified proteins were demonstrated by detection of CoA. CoA was released from the proteins by dithioerythritol treatment under denaturing conditions and was identified by (a) its retention time on HPLC, (b) its absorption spectrum and (c) its activity in a CoA-specific assay. This CoA represents protein-bound CoA and, in addition, protein-bound palmitoyl-CoA when MgATP was also present in the in vitro assay. The detection of immunoreactive proteins using mono-specific anti-CoA antibodies exclusively identifies CoA-modified proteins. The specificity of these antibodies can be used to identify both endogenously occurring CoA-modified proteins and proteins that have been modified in the in vitro assay. An intact thiol group of CoA is an essential precondition for the modification to occur.

Turnover and transformation of mitochondrial acetyl-CoA acetyltransferase into CoA-modified forms.

Rat liver mitochondrial acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase, EC 2.3.1.9) exists additionally in the CoA-modified forms A1 and A2. After a pulse of radioactivity using [35S]methionine in hepatocytes, the highest radioactivity was obtained in the unmodified enzyme. Over the chase time, the radioactivity in the unmodified enzyme decreased, but simultaneously increased in both CoA-modified forms, thus proving that the fully active unmodified enzyme exists before the partially active modified forms A1 and A2. Also, the specific radioactivity (ratio % radioactivity/% immunoreactive area) of A1 > A2 demonstrates a sequential CoA modification of form A1 to form A2. Acetyl-CoA acetyltransferase was degraded with an apparent half-life of 38.0 h: the modified forms A1 and A2 have half-lives of 24.5 and 7.2 h. The physiological meaning of the CoA modification of acetyl-CoA acetyltransferase is not yet understood.

Differentiation of the four viruses of the sugarcane mosaic virus subgroup based on cytopathology.

A cytological comparison has been made of representative isolates of johnsongrass mosaic (JGMV), maize dwarf mosaic (MDMV), sorghum mosaic (SrMV) and sugarcane mosaic (SCMV) viruses. These four viruses now encompass the complex of virus strains which were formerly considered as strains of sugarcane mosaic and/or maize dwarf mosaic viruses. The structure of the cytoplasmic cylindrical inclusions induced by these viruses, together with other cytological alterations, allow the four viruses to be distinguished. Pinwheels, scrolls and laminated aggregates were produced only by SCMV whereas JGMV, MDMV, and SrMV produced only pinwheels and scrolls. SrMV produced amorphous cytoplasmic inclusions which are not produced by JGMV and MDMV. The latter two were rather similar in cytological effects except that the SCMV-JG (U.S.A.) isolate of MDMV produced aggregates of needle-like structures in the cytoplasm which were not found with JGMV and the other MDMV isolates. The specific cytological effects induced by these viruses thus corroborate the recent classification of these viruses based mainly on the properties of the coat-protein gene, the 3' noncoding nucleotide sequences, and host reactions.

Identification of the CoA-modified forms of mitochondrial acetyl-CoA acetyltransferase and of glutamate dehydrogenase as nearest-neighbour proteins.

A 52 kDa protein could only be co-purified with the CoA-modified forms of acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase) (EC 2.3.1.9) from rat liver mitochondria. Immunoprecipitations of these modified forms with anti-(acetyl-CoA acetyltransferase) IgG or anti-(52 kDa protein) IgG yielded, in addition to the appropriate proteins, the 52 kDa protein or the CoA-modified form of acetyl-CoA acetyltransferase (41 kDa) respectively. This was demonstrated by SDS/PAGE and immunoblots. The modified forms containing the 52 kDa protein could be cross-linked by 1,5-difluoro-2,4-dinitrobenzene to a high-molecular-mass complex containing both the 41 kDa and 52 kDa proteins. The 52 kDa protein was identified as mitochondrial glutamate dehydrogenase (EC 1.4.1.3) by amino acid sequence analysis. The results of co-immunoprecipitation and cross-linking characterize the CoA-modified forms of acetyl-CoA acetyltransferase and the glutamate dehydrogenase as nearest-neighbour proteins.

Evidence for an in vivo modification of mitochondrial proteins by coenzyme A.

Following denaturation of mitochondrial proteins by sodium dodecyl sulfate, a [1-14C]pantothenic acid-derived radioactivity proved to be acid precipitable in the outer membrane, the intermembrane space, the inner membrane and in the matrix of rat liver mitochondria, where it had the highest specific radioactivity of 541 +/- 29 cpm/100 micrograms protein. This tightly and/or covalently bound protein radioactivity could be released by incubation in the presence of dithioerythreitol; it was identified as [14C]coenzyme A by its HPLC retention time, its absorption spectrum and its radioactivity. This acid-stable and thiol-labile coenzyme A-binding apparently refers to specific protein binding sites. With the purified, homogeneous mitochondrial matrix enzymes acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase) (EC 2.3.1.9, acetyl-CoA:acetyl-CoA C-acetyltransferase) and 3-oxoacyl-CoA thiolase (EC 2.3.1.16) coenzyme A was found exclusively, e.g., in the modified, partially-active forms A1 und A2 of acetyl-CoA acetyltransferase and not in the unmodified fully-active enzyme. Thus it is evident that this coenzyme A modification is transient. We suggest that coenzyme A-modification is a signal involved in the assembly or the degradation process of distinct mitochondrial matrix proteins.

Barley yellow mosaic virus (BaYMV) and BaYMV-M: two different viruses.

Serological and physical properties of isolated particles as well as reactions of barley cultivars after virus inoculation showed that the yellow disease of barley is caused by different viruses. Results summarized in this paper suggest that the European isolates BaYMV-So and BaYMV-NM are closely related to, or identical with, BaYMV-J first reported from Japan, whereas BaYMV-M differs in several properties. Therefore, it seems justified to describe BaYMV-M as a separate virus tentatively designated barley mild mosaic virus.

Identification of [1-14C]pantothenic-acid-mediated modified mitochondrial proteins.

The in vivo administration of [1-14C]pantothenic acid, which is the precursor of coenzyme A, resulted in the radioactive labelling of several mitochondrial proteins in rat liver. The incorporated radioactivity could be released by glutathione or 2-mercaptoethanol. Two mitochondrial matrix proteins acetyl-CoA acetyltransferase (liver and heart), an enzyme involved in the biosynthesis or degradation of ketone bodies, and 3-oxoacyl-CoA thiolase (liver), a protein participating in fatty acid oxidation were identified as modified proteins. The radioactivity was localized exclusively in forms A1 and A2 indicating that these forms represent the modified states of the acetyl-CoA acetyltransferase protein. Kinetics of incorporation of radioactivity revealed an accumulation of the modified forms. The ratio of specific radioactivities of A2 compared to A1 was 2.41 +/- 0.15 (n = 10). After in vivo labelling with [14C]leucine, the specific radioactivity of acetyl-CoA acetyltransferase depended on the state of the enzyme protein. The unmodified enzyme exhibited a lower specific radioactivity than its modified forms suggesting different turnover rates of these proteins.

Mitochondrial acetyl-CoA acetyltransferase in liver and extrahepatic tissues: role of modification by coenzyme A.

The influence of clofibrate and di(2-ethylhexyl)phthalate on mitochondrial acetyl-CoA acetyltransferase (acetyl-CoA: acetyl-CoA C-acetyltransferase, EC 2.3.1.9), the rate-limiting ketogenic enzyme, which can be modified and inactivated by CoA, was investigated. In fed rats, both compounds induced a doubling of ketone bodies in the blood and, moreover, an increase by about 13% in the hepatic relative amount of the unmodified, i.e., the most active form of the enzyme (immunoreactive protein). This shift would account for an elevation of overall enzyme activity by about 5% only. Thus, the CoA modification of mitochondrial acetyl-CoA acetyltransferase did not explain the entire augmentation of ketone bodies. However, clofibrate and di(2-ethylhexyl)phthalate also increased the immunospecific protein and enzyme activity by approx. 2- and 3-fold, respectively. These effects were observed in liver, but not in several extrahepatic tissues.

Mitochondrial acetyl-CoA acetyltransferase in various organs from rat: form patterns and coenzyme-A-mediated modification.

The mitochondrial acetyl-CoA acetyltransferase (acetyl-CoA:acetyl-CoA C-acetyltransferase, EC 2.3.1.9), which is involved in the biosynthesis or degradation of ketone bodies, was directly demonstrated in organ extracts applying a two-step chromatography-immunoelectrophoresis method. In liver, the enzyme can be shown in at least three forms: in an unmodified state, designated as AAT, and in the CoASH-modified forms A1 and A2, in amounts of 51.5 +/- 5.0%, 39.4 +/- 4.8% and 9.1 +/- 2.7% (areas of immunoprecipitation), respectively. This pattern, which could not be altered by a treatment with glutathione, resembles that of mitochondrial acetyl-CoA acetyltransferase in extrahepatic tissues. However, the proportion of the unmodified enzyme (AAT) is lower as compared to those in other tissues such as brain (81.5 +/- 4.4%). CoASH-modification and transformation into modified forms, which equal naturally occurring forms, can be demonstrated in vitro with acetyl-CoA acetyltransferase from both liver and brain. Thus CoASH-modification of mitochondrial acetyl-CoA acetyltransferase seems to be a process of general importance.

On the mechanism of the chemical modification of the mitochondrial acetyl-CoA acetyltransferase by coenzyme A.

The liver mitochondrial acetyl-CoA acetyltransferase (acetyl-CoA:acetyl-CoA C-acetyltransferase, EC 2.3.1.9), is involved in ketone body synthesis. The enzyme can be chemically modified and inactivated by CoASH and also by CoASH-disulfides provided glutathione is present. The unmodified enzyme shows in its denatured state 7.95 +/- 0.44 sulfhydryl groups per enzyme and in its native state 3.92 +/- 0.34 sulfhydryl groups which react with Ellmann's reagent. The modified enzyme reveals in its native state also 4.07 +/- 0.25 sulfhydryl groups per enzyme, but in its denatured state 9.10 +/- 0.51 sulfhydryl groups could be detected. Approximately four sulfhydryl groups per enzyme, unmodified or modified, can be alkylated by iodoacetamide. These results prove for each subunit the existence of two sulfhydryl groups and suggest the existence of two disulfide bridges. The CoASH modification, which should proceed at one of these disulfide groups, prevents subsequent acetylation of the enzyme and is drastically reduced in the iodoacetamide-alkylated enzyme. In the demodification of the modified enzyme, the CoASH is set free as a mixed disulfide with glutathione.

Modulation of rat-liver mitochondrial acetyl-CoA acetyltransferase activity by a reversible chemical modification with coenzyme A.

The mitochondrial acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase, EC 2.3.1.9) is involved in ketone body biosynthesis. In its unmodified state, referred to as transferase B in former publications (Huth, W. (1981) Eur. J. Biochem. 120, 557-562), the enzyme is characterized by the highest specific activity of 21.65 mumol/min per mg protein (direction of acetoacetyl-CoA synthesis); several forms of the enzyme with lower specific activities result from chemical modification by an apparent covalent binding of CoASH. The chemical modification results in an inactivation of the enzyme: a 2 h incubation with 0.2 mM CoASH at pH 8.1 at 30 degrees C inactivates up to 95%. Both processes, the CoASH-binding and the resulting inactivation, can be simultaneously reversed by treatment with glutathione. The specificity of inactivation is limited to CoASH and the intact sulfhydryl group is a prerequisite for this process. The enzyme exhibits a limited number (n = 3.2) of high-affinity (Ka = 26.7 microM) specific binding sites for CoASH. The inactivation-reactivation cycle of acetyl-CoA acetyltransferase by CoASH and glutathione may involve a protein disulfide-thiol exchange and represents a mode of control in modulating the amount of active enzyme.

Regulation of ketogenesis. Mitochondrial acetyl-CoA acetyltransferase from rat liver: initial-rate kinetics in the presence of the product CoASH reveal intermediary plateau regions.

The analysis of the initial-rate kinetics of the liver mitochondrial acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase) in the direction of acetoacetyl-CoA synthesis under product inhibition was performed. 1. Acetyl-CoA acetyltransferase shows a hyperbolic response of reaction velocity to changes in acetyl-CoA concentrations with an apparent Km of 0.237 +/- 0.001 mM. 2. CoASH is a (non-competitive) product inhibitor with a Kis of 22.6 microM and shifts the apparent Km for acetyl-CoA to the physiological concentration of this substrate in mitochondria (S0.5 = 1.12 mM in the presence of 121 microM CoASH). 3. CoASH causes a transformation of the Michaelis-Menten kinetics into initial-rate kinetics with four intermediary plateau regions. 4. The product analogue desulpho-CoA triggers a negative cooperativity as to the dependence of the reaction velocity on the acetyl-CoA concentration. These product effects drastically desensitize the acetyl-CoA acetyltransferase in its reaction velocity response to the acetyl-CoA concentrations and simultaneously extend the substrate dependence range. Thus a control of acetoacetyl-CoA synthesis by the substrate is established over the physiological acetyl-CoA concentration range. We suggest that this control mechanism is the key in establishing the rates of ketogenesis.

The charge heterogeneity of the mitochondrial acetyl-CoA acetyltransferase from rat liver.

The charge heterogeneity of the mitochondrial acetyl-CoA acetyltransferase (EC 2.3.1.9) referred to transferases A and B, seems to be preformed in vivo and can be demonstrated in vitro by a spontaneous transformation of transferase A into transferase B. These two enzymes, although remarkably similar in amino acid composition, show structural dissimilarities. This becomes evident from their tryptic maps, which are substantially different. Isoelectric focusing in the presence of urea confirms the charge heterogeneity of the mitochondrial acetyl-CoA acetyltransferase by indicating different patterns of protein bands for transferases A and B. Transferase B lacks the protein band with an isoelectric point of 7.2 which is normally shown with transferase A. However, this 7.2-pI protein band can be demonstrated after a [32P]CoASH treatment of transferase B in the presence of urea by protein staining and by autoradiography. This change in the isoelectric focusing band pattern after interaction of the subunits with CoASH in interpreted as being the result of an apparently covalent secondary modification of the protein side chains. The CoASH-modification may be the only molecular basis of the acetyl-CoA acetyltransferase charge heterogeneity, a veiw, which is further substantiated by the CoASH-mediated transformation of transferase B into transferase A. An additional heterogeneity of the enzyme as caused by a limited proteolysis seems unlikely but cannot be definitely excluded.

Threshold noise and the laser transient.

The energy in a laser cavity at threshold affects the time required for the laser to go from threshold to saturation. By determining the statistical distribution of laser turn-on times, i.e., the time required for the laser to undergo its transient from threshold to saturation, the noise distribution in the cavity can be calculated. A phenomenological model is used to analyze the low-level noise in a laser cavity based on the distribution of turn-on times of a pulsed laser. The results of this analysis are used to study the effects of injecting a signal from a cw laser into the cavity of the pulsed laser. A small injected signal shortens the laser transient and changes the shape of the distribution of turn-on times. The method used allows examination of the statistical properties of photons in the cavity without the need for photon counting.

Immunochemical aspects, molecular and kinetic properties of multiple forms of acetyl-CoA acetyltransferase from rat liver mitochondria.

Acetyl-CoA acetyltransferase (EC 2.3.1.9) from rat liver mitochondria, which catalyzes the first step in the biosynthesis of ketone bodies, exists in two forms, designated transferase A and transferase B. Both transferases showed immunochemical cross-reactivity, but are immunologically unrelated to cytosolic acetyl-CoA acetyltransferase activity and the mitochondrial acetyl-CoA acyltransferase from rat liver. The transferases A and B were estimated to have molecular weights of 151 000 in the absence and 40 000 in the presence of sodium dodecyl sulfate. They differ with respect to charge states and multiplicity of forms as indicated by isoelectric focusing. Transferase A appeared in two forms with isoelectric points of 8.4 and 9.1, whereas transferase B represents a stable protein state with an isoelectric point of 9.0. Kinetic analysis of the reactions leading to acetoacetyl-CoA synthesis revealed saturation curves with multiple intermediary plateaus, indicating a complex kinetic behaviour. The data presented are interpreted as representing a microheterogeneity of forms of the mitochondrial acetyl-CoA acetyltransferase. The kinetic properties exhibited suggest a role for this microheterogeneity in the regulation of ketogenesis.