Protein phosphorylation and hormone action

Although the scheme hormone leads to raised cyclic AMP levels leads to activated protein kinase leads to phosphorylated protein leads to physiological response may represent an outline for the action of several hormones, in the best understood example, namely regulation of glucogen metabolism in mammalian muscle, the picture is more complex. Modification of phosphorylase kinase by cyclic AMP-dependent protein kinase, after stimulation by adrenaline, leads to phosphorylation of the enzyme at two sites. Activation is associated exclusively with the phosphorylation of the primary site, but the secondary phosphorylation indirectly antagonizes the primary phosphorylation in that it is necessary to render the primary site susceptible to dephosphorylation. The recent separation of two distinct phosphorylase kinase phosphatases specific for the two sites shows that reversal of the hormonal stimulation is controlled by the relative activities of two enzymes with opposing functions. Glycogen synthetase, which is phosphorylated and inactivated by cyclic AMP-dependent protein kinase, is also under the control of insulin. Although insulin appears to stimulate glycogen synthetase by reversal of the inactivation catalysed by the cyclic AMP-dependent protein kinase, tissue cyclic AMP concentrations do not alter. The recent identification of a second glycogen synthetase kinase, unaffected by cyclic AMP, therefore raises the possibility that insulin action may also be mediated through phosphorylation-dephosphorylation mechanisms, which antagonize those mediated through cyclic AMP-dependent protein kinase.

Molecular criteria for genus and species discrimination within the family Potyviridae

A phylogenetic analysis of the optimised nucleotide (nt) alignment of the entire ORFs of a representative of each fully-sequenced species in the family Potyviridae provided strong support for several subgroups within the genus Potyvirus. A complete set of two-way comparisons was done between the sequences for the entire ORF and for each gene amongst all the 187 complete sequences from the family. Most species had 50-55% nt identity to other members of their genus in their ORFs but there were significant groups of more closely related species and species demarcation criteria were <76% nt identity and <82% amino acid identity. The corresponding thresholds for species demaracation using nt identity values for the individual genes ranged from 58% (P1 gene) to 74-78% (other genes) although a few comparisons between different species exceeded these values. For the entire ORF, genus demarcation criteria were <46% nt identity but this did not separate rymoviruses from potyviruses. Comparisons in the CI gene most accurately reflected those for the complete ORF and this region would therefore be the best for diagnostic and taxonomic studies if only a sub-portion of the genome is to be sequenced. Further comparisons were then made using all the 1220 complete capsid protein (CP) genes. These studies suggest that 76-77% nt identity is the optimal species demarcation criterion for the CP. The study has also helped to allocate the correct virus name to some sequences from the international databases that currently have incorrect or redundant names. The taxonomic status of the current genus Rymovirus and of three unassigned species in the family is discussed. Significant discontinuities in the distributions within and between the currently defined species suggest that the continuum of variation that is theoretically available is constrained or disrupted by molecular barriers that must have some biological significance.

The new plant virus family Flexiviridae and assessment of molecular criteria for species demarcation

The new plant virus family Flexiviridae is described. The family is named because its members have flexuous virions and it includes the existing genera Allexivirus, Capillovirus, Carlavirus, Foveavirus, Potexvirus, Trichovirus and Vitivirus, plus the new genus Mandarivirus together with some related viruses not assigned to any genus. The family is justified from phylogenetic analyses of the polymerase and coat protein (CP) sequences. To help to define suitable molecular criteria for demarcation of species, a complete set of pairwise comparisons was made using the nucleotide (nt) and amino acid (aa) sequences of each fully-sequenced gene from every available accession in the family. Based on the distributions and on inspection of the data, it was concluded that, as a general rule, distinct species have less than ca. 72% identical nt or 80% identical aa between their entire CP or replication protein genes.

A new potyvirus from tuberose ( Polianthes tuberosa) in China

Tuberose plants with mild mottle symptoms, growing in a glasshouse in Hangzhou, China, contained virions and inclusion bodies typical of a potyvirus. The virus was mechanically transmitted to tuberose but not to 14 other test plant species. A fragment of 4607 nucleotides, corresponding to the 3'-half of a typical potyvirus was amplified by RT-PCR using degenerate primers and sequenced. The most similar sequence in the databases was that of Tuberose mild mosaic virus (TuMMV) from Taiwan and this was the only virus significantly related to it in phylogenetic analyses. The new sequence had 71.1% nt and 76.6% aa identity to TuMMV in the coat protein. Western blot analyses using antisera raised to expressed coat protein showed that the two viruses were serologically related. Although there are no substantial biological data to distinguish the Hangzhou isolate from TuMMV, the molecular difference between the two virus isolates is similar to, or slightly greater than, that between several pairs of well-established potyvirus species. These results therefore suggest that the Hangzhou isolate should be regarded as a new member of the genus Potyvirus, and we have tentatively named it Tuberose mild mottle virus.

A virus related to soybean mosaic virus from Pinellia ternata in China and its comparison with local soybean SMV isolates

A potyvirus isolated from Pinellia ternata in China was characterised and shown to be related to Soybean mosaic virus (SMV). The virus was pathogenic on P. ternata and some soybean cultivars, whereas the local soybean SMV isolate HH5 did not infect P. ternata. Western blot experiments demonstrated a serological relationship between the virus from Pinellia, SMV and Watermelon mosaic virus (WMV). The complete nucleotide sequences of the Pinellia virus (isolate P-1, 9735 nt) and of the Chinese soybean SMV isolates HH5 (9585 nt) and HZ (9588 nt) were determined. A 1733 nt sequence at the 3'-terminus of a second isolate from Pinellia (isolate P-2) was also determined. The predicted polyprotein of isolate P-1 has 83% amino acid (aa) identity with those of published SMV sequences. In many parts of the genome, aa identity was about 90% but it was much lower in the P1 protein region (24-29%), where it more closely resembled Dasheen mosaic virus (62%). The partial sequence of isolate P-2 had 91% nt identity to P-1 and both isolates resembled a recent sequence in the public databases (AF469171) wrongly named Zantedeschia mosaic virus. The two complete SMV soybean sequences had 93-95% nt identity with those of the previously sequenced isolates and >97% amino acid identity. Phylogenetic analysis and comparisons of coat proteins suggest that the Pinellia, WMV and SMV potyviruses should probably be treated as strains of the same species.

Detection and classification of allexiviruses from garlic in China

Degenerate primers for RT-PCR were designed and used to amplify genome fragments ( c. 750 nt in the coat protein-ORF6 region) of allexiviruses from a total of 28 garlic samples from 24 provinces in China. Many samples contained more than one distinct sequence. A total of 60 different sequences were obtained. Phylogenetic analysis and two-way comparisons were used to assess the status of the sequences and to re-examine the criteria for distinguishing species within the genus. Most of the sequences could be allocated to either Garlic virus D or Garlic virus X on the basis of sequence similarity but some appeared to be intermediate between existing species. There were no sequences of Garlic virus C or Shallot virus X. A comparison with the related genera Carlavirus, Foveavirus and Potexvirus suggests that the published allexivirus species demarcation criteria may have been drawn too tightly and should be re-examined.

Codon usage bias amongst plant viruses

An internet database (DPVweb) was established containing details of all sequences of viruses, viroids and satellites of plants that are complete or that contain at least one complete gene (n>4600). The start and end positions of each feature (genes, non-translated regions etc) were recorded and checked for accuracy. Client software was written to enable easy selection of sequences and features of a chosen virus and to analyse codon usage bias. Codon usage was analysed for each gene of one example of each fully-sequenced plant virus. There were large differences in codon preferences, related to the nucleotide composition of the genome, particularly the GC content of the third codon position. There was no effect of gene size on codon bias. Genes from the same genome usually had similar coding strategies except where constrained by the overlap of reading frames. Although some synonymous codons were consistently used with low frequency by both plants and viruses, viruses were not generally adapted to use (or avoid) those codons most frequently used by their host plants and there was no obvious association with the type of transmission. Mutational bias, rather than translational selection appears to account for the majority of the variation detected. The software is available at http://www.dpvweb.net/analysis/codons.php.

Occurrence and sequences of Lily mottle virus and Lily symptomless virus in plants grown from imported bulbs in Zhejiang province, China

Degenerate primers were used to amplify virus sequences from imported lilies in Zhejiang province, China. Two viruses, Lily mottle virus (LMoV, genus Potyvirus) and Lily symptomless virus (LSV, genus Carlavirus) were detected, purified and completely sequenced from a mixed infection in a plant raised from bulbs imported from the Netherlands. The sequence of LMoV was 9644 nt long and encoded a polyprotein of 3095 amino acids with a calculated M(r) of 351.0 kDa that had only 45.1-54.4% identity to other completely sequenced potyviruses. Phylogenetic analysis of the complete polyproteins of members of the genus demonstrated that LMoV was distantly grouped with LYSV, BYMV and ClYVV. Two partial LMoV sequences from different cultivars were identical to one another and very similar (98.3% identical nucleotides) to the corresponding region of the complete sequence. Analysis of the coat protein sequences of LMoV isolates revealed two subgroups, corresponding to the earlier "Tulip breaking virus lily strain" and "Tulip band breaking virus" isolates. Our newly-determined isolates showed an extremely close relationship to the first of these. The LSV sequence was 8393 nucleotides long and had the typical carlavirus genome organization. The ORF1 protein was most closely related to that of Blueberry scorch virus (57.2% identical amino acids). Sequences of 1796 nt at the 3'-end of three additional LSV isolates from different cultivars were very similar (>98% identical nucleotides) to the corresponding region of the complete sequence. This is the first report of complete sequences for LMoV and LSV.

TMCompare: transmembrane region sequence and structure

TMCompare is an alignment and visualization tool for comparison of sequence information for membrane proteins contained in SWISS-PROT entries, with structural information contained in PDB files. The program can be used for: detection of breaks in alpha helical structure of transmembrane regions; examination of differences in coverage between PDB and SWISS-PROT files; examination of annotation differences between PDB files and associated SWISS-PROT files; examination and comparison of assigned PDB alpha helix regions and assigned SWISS-PROT transmembrane regions in linear sequence (one letter code) format; examination of these differences in 3D using the CHIME plugin, allowing; analysis of the alpha and non-alpha content of transmembrane regions.

AVAILABILITY

TMCompare is available for use through selection of a query protein via the internet (http://www.membraneproteins.org/TMCompare)

CONTACT

tmcompare@membraneproteins.org

Plant virus transmission by plasmodiophorid fungi is associated with distinctive transmembrane regions of virus-encoded proteins

Computer analysis of published sequence data has consistently identified two complementary transmembrane domains in the coat protein readthrough domains of benyviruses, furoviruses and pomoviruses and in the P2 proteins of bymoviruses. These viruses differ in genome organisation but are all transmitted by plasmodiophorid fungi. The second domain is absent or disrupted in naturally-occurring deletion mutants that cannot be fungally-transmitted. In a non-transmissible substitution mutant of Beet necrotic yellow vein virus [Tamada et al. (1996) J Gen Virol 77: 1359-1367], the alignment of the helices is disrupted. From conserved patterns detected in transmembrane helix sequences and calculated relative helix tilts, structural arrangements consistent with tight packing of transmembrane helices were identified. These included ridge/groove arrangements between the two helices and strong electrostatic associations at the interfacial regions of the membrane. The data strongly suggest that these transmembrane helices facilitate the movement of virus particles across the fungal membrane.

Molecular analysis of barley yellow mosaic virus isolates from China

The complete sequences of both RNAs of an isolate of barley yellow mosaic virus from Yancheng, Jiangsu province, China, were determined. The sequences resembled those of an isolate from Japan (96.8% identical nucleotides for RNA1; 95.7% for RNA2) more closely than one from Germany (93.9 and 91.0%, respectively). The greatest differences between the Chinese and Japanese isolates were in the 5'-UTRs of RNAs 1 and 2 (88.9 and 91.6% identical nucleotides, respectively) and there were also some other regions of difference in P1 (RNA2) and P3, CI, NIa and the 5' end of the coat protein (CP) (RNA1). Molecular differences between isolates from ten sites widely distributed in Eastern China were studied by sequencing RNA regions coding for the CP (RNA1) and the N-terminus of the P2 protein (RNA2). The P2 fragment was more variable than the CP, and phylogenetic analysis of both regions showed that Asian and European isolates formed distinct clusters. Differences between isolates were also revealed by single-strand conformation polymorphism of reverse transcription-polymerase chain reaction products, spanning the full lengths of both RNA1 and RNA2. However, molecular variations between isolates could not be linked to earlier results showing differences in cultivar response.

Sequences of European wheat mosaic virus and oat golden stripe virus and genome analysis of the genus furovirus

The complete nucleotide sequences of both RNAs of oat golden stripe virus (OGSV) and a wheat-infecting furovirus isolate from France, previously thought to be soil-borne wheat mosaic virus (SBWMV), have been determined. Both viruses had a similar genomic organisation to SBWMV and Chinese wheat mosaic virus, the two other furoviruses previously sequenced but had <70% nucleotides identical to them. The French isolate has been named European wheat mosaic virus (EWMV). Phylogenetic analyses supported the recognition of these isolates as distinct viruses in the genus Furovirus. Analysis of the coat protein readthrough domain on RNA2 of all furoviruses strongly predicts two mutually compatible conserved transmembrane domains that may be significant for fungus transmission. The second of these regions is eliminated by a deletion in the isolate of OGSV studied. Leaky opal (UGA) stop codons occur on both RNAs of all four furoviruses characterised and, in common with most other leaky opal codons identified in plant viruses, they are followed by a CGG codon.

Complete sequence and genome properties of Chinese wheat mosaic virus, a new furovirus from China

The complete nucleotide sequence of a virus infecting winter wheat in Shandong province, China has been determined. This was previously thought to be soil-borne wheat mosaic virus but, while the two viruses are related, they are only 75% (RNA1) and 63% (RNA2) identical at the nucleotide level, while the amino acid sequences share from 62% (19 kDa RNA2 product) to 84% (RNA1 replicase) identity. The analysis shows that the Chinese virus should be considered a new member of the genus Furovirus and has been named Chinese wheat mosaic virus (CWMV). A Cys-Gly ... Cys-Gly-X-X-His amino acid pattern was identified in the cysteine-rich protein of CWMV and those of several other plant virus genera, which seems likely to have some functional significance.

Complete RNA1 sequences of two UK isolates of barley mild mosaic virus: a wild-type fungus-transmissible isolate and a non-fungus-transmissible derivative

The complete RNA1 sequences of two isolates (fungus transmissible and non-fungus transmissible) of barley mild mosaic virus (BaMMV) were obtained. The two isolates' RNA1 sequences had very high sequence identity (99.3%), and of the 15 amino acid differences (out of 2258) between the putative polyproteins, 11 were conservative and unlikely to affect the structure or function of the protein. The remaining amino acid differences were thought unlikely to affect fungus transmission because they occur in the CI- and NIb-coding regions. This strongly suggests that the P73 protein of RNA2 (which has a 364-aa deletion in the non-fungus-transmissible isolate) is involved in fungus transmission of BaMMV.

A large duplication in the 3'-untranslated region of a subpopulation of RNA2 of the UK-M isolate of barley mild mosaic bymovirus

The UK-M isolate of the bipartite barley mild mosaic bymovirus (BaMMV UK-M) cannot be fungally transmitted, and has previously been shown to have a 1092 nt deletion in the coding region of RNA2. We now report, using sequence and reverse transcriptase-polymerase chain reaction (RT-PCR) data, that a subpopulation of BaMMV UK-M RNA2 contains a direct imperfect sequence repeat of 552 nt in the 3' untranslated region. The secondary structure of the 3' end of RNA2, and its possible effects on replication of the virus, are also discussed.

Single-strand conformation polymorphism analysis of RT-PCR products of UK isolates of barley yellow mosaic virus

Single-strand conformation polymorphism (SSCP) analysis of the bipartite genomes of several UK isolates of barley yellow mosaic virus (Ba YMV) was done using fragments of cDNA amplified by RT-PCR. Isolates differed in their SSCP patterns in several regions, but in no case was the pattern able to distinguish between common and resistance-breaking strains. In regions where the nucleotide sequences of UK isolates had been determined, there was no simple relationship between numbers of nucleotide differences and SSCP patterns: differences of only 2 or 3 nucleotides (nt) gave different SSCP patterns, whereas differences of as many as 29 nt did not. Although SSCP analysis has some potential as a rapid and sensitive tool for distinguishing virus isolates, differences detected do not necessarily relate to biological properties and the results are highly dependent on gel conditions.

Sequence analysis of wheat and oat furovirus capsid protein genes suggests that oat golden stripe virus is a strain of soil-borne wheat mosaic virus

In northern blots, cDNA probes prepared to soil-borne wheat mosaic virus (SBWMV) RNA-1 and RNA-2 hybridized to RNA-1 and RNA-2, respectively, from a UK isolate of oat golden stripe virus (OGSV), as well as to their homologous RNAs. RT-PCR was used to amplify, clone and sequence a region of about 750 nucleotides spanning the capsid protein gene and part of the readthrough protein on RNA-2 from OGSV, a French isolate of SBWMV and two stable deletion mutants (Lab1 and Okl-7) of SBWMV isolates from Nebraska and Oklahoma respectively. There was very high (96.7-99.1%) nucleotide homology between all these sequences and the wild-type SBWMV sequences from Nebraska and Oklahoma. OGSV was more similar to SBWMV from France and Nebraska than were any of the isolates to SBWMV from Oklahoma. Of the few differences in the deduced amino acid sequences of the capsid proteins from the different isolates, OGSV differed from all SBWMV isolates only in one amino acid (isoleucine for valine at position 88). The high degree of similarity suggests that OGSV may best be classified as an oat strain of SBWMV.

The complete nucleotide sequence of RNA-2 of a fungally-transmitted UK isolate of barley mild mosaic bymovirus and identification of amino acid combinations possibly involved in fungus transmission

The complete nucleotide sequence of RNA-2 of a fungally-transmitted UK isolate of barley mild mosaic bymovirus (BaMMV isolate UK-F) was determined and compared with other published sequences, particularly UK-M, an isolate derived from the same source but which has been mechanically passaged for several years, has a deletion of about 1 kb and cannot be fungally transmitted. From an alignment of the BaMMV RNA-2 encoded protein with that for barley yellow mosaic bymovirus (BaYMV), several regions of consistent homology were identified and extensive searches made for similarities with the proteins of other fungally-transmitted viruses, especially amongst the furovirus capsid readthrough proteins which seem especially prone to deletion and which have already been implicated in fungus transmission. The amino acid combinations ER (glutamic acid-arginine) or QR (glutamine-arginine) were found consistently in all of the viruses. They occurred in positions predicted to be on the outside of the protein, and therefore available for interaction with the fungus vector, and were also within the regions prone to spontaneous deletion. In view of the lack of other structural or sequence homologies, it is suggested that these motifs are strong candidates for involvement in fungus transmission.

An analysis of differential display shows a strong bias towards high copy number mRNAs

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Molecular characterisation of UK isolates of barley yellow mosaic bymovirus

Several isolates of barley yellow mosaic virus (BaYMV) from different sites in the UK, including some that were virulent on European resistant winter barley cultivars (resistance-breaking strain: BaYMV-2) and some that were not, were examined by RT-PCR, restriction mapping and sequencing of selected parts of the virus genome. Nucleotide and predicted amino acid sequences were determined for the 5'-terminal region, part of the NIa coding region and the coat protein coding region on RNA 1 and an area at the N-terminus of the 70-kDa protein coding region on RNA 2. The sequences differed from those previously reported for a BaYMV isolate from Japan and for two German isolates, one of which was of the BaYMV-2 strain. There were no strain-specific amino acid differences and the few, non-consecutive, nucleotide differences detected were probably not significant and were insufficient to develop a rapid diagnostic test to distinguish BaYMV-2 from other isolates. Restriction mapping of RNA 2 cDNA again showed no consistent strain-related differences. The differences previously reported between the two German isolates are probably not strain-related.

Cloning and sequence analysis of RNA-2 of a mechanically transmitted UK isolate of barley mild mosaic bymovirus (BaMMV)

A mutant of the 'Streatley' isolate of barley mild mosaic bymovirus was selected from the original field isolate by repeated mechanical inoculation. Unlike the wild-type barley mild mosaic virus, which is transmitted by the soilborne fungus Polymyxa graminis, the mutant could not be transmitted by this vector. RNA-2 of the mutant virus was shorter than that of the wild-type virus suggesting that a deletion of part of the genome segment had occurred. The nucleotide sequence of the mutant RNA-2 was determined and revealed a high degree of homology with the RNA-2 of a German BaMMV field isolate. The deletion comprises 1092 nucleotides and is located in the 3'-terminal part of the coding region. The 34-kDa truncated form of the C-terminal protein is less than half the size of the corresponding protein of full-length BaMMV RNA-2. Taken together, the sequence data and results of biological experiments suggest an essential role of the C-terminal protein for fungus transmission of BaMMV.

Nucleotide sequence of beet cryptic virus 3 dsRNA2 which encodes a putative RNA-dependent RNA polymerase

The nucleotide sequence of a DNA copy of beet cryptic virus 3 double-stranded RNA2 was determined, and one strand was found to contain a single long open reading frame of 1431 nucleotides which encoded a putative polypeptide containing 478 amino acid residues with an M(r) of 54.9K. This polypeptide contained conserved amino acid sequence motifs found in the genes that encode putative RNA-dependent RNA polymerases of other RNA viruses.

Changes with time in the distribution of virus and PR protein around single local lesions of TMV infected tobacco

ELISA was used to determine PR la protein and TMV accumulation in local necrotic lesions produced on salicylic acid and water sprayed Nicotiana tabacum cv Xanthi-nc leaves. The amount of PR la protein produced is the result of an interaction between the salicylic acid treatment and lesion growth. The implication of these observations for experiments investigating the relationship between PR proteins and resistance are discussed.The distribution of TMV and PR la protein in and around single local necrotic lesions up to 14 days after inoculation was measured by ELISA. The highest concentration of TMV was in the centre of the lesion and decreased rapidly with distance from the centre. In contrast there was very little PR la protein in the centre of the lesion, the largest amounts were just outside the centre, and the concentration then decreased with distance from the centre. This is the distribution that might be expected for a substance closely associated with the restriction of virus spread.

The chemical induction of PR (b) proteins and resistance to TMV infection in tobacco

Aspirin injected into Xanthi-nc tobacco leaves induces the production of PR protein and resistance to TMV. The concentration of PR protein and resistance increases with increasing aspirin concentration, up to a plateau. 2-Thiouracil and dioxohexahydrotriazine also induce PR protein when injected into tobacco leaves. Barium and manganese salts induced PR protein, but those of eight other cations did not. Certain salts were phytotoxic but did not induce PR protein, confirming that the production of PR protein is not a non-specific stress response.

Biochemical and serological characterization of b-proteins fromNicotiana species

Proteins associated with the hypersensitive response (b-proteins) were purified from variousNicotiana species and compared biochemically and serologically. The method developed to purify proteins b1, b2 and b3 ofN. tabacum cv. Xanthi-nc was used to purify b-proteins present inN. sylvestris (b0, b1 and b3) andN. tomentosiformis (b2), the parental species ofN. tabacum, and b1″ from bothN. glutinosa andN. debneyi. Ultracentrifugation and amino acid analysis of some of these proteins has shown that they are very similar and that they are all monomers in their native form (mol wt = 15 700 for b0, b1, b2 and b3; mol wt = 13 800 for b1″).Based on their reactions to an antiserum produced against protein b1 ofN. tabacum cv. Xanthi-nc, 3 serological groups can be recognized which are independent of the source species (I) b0 and b1, (II) b1″ and b2, (III) b3. Thus, proteins in the same serological group but from different species are more closely related than the b-proteins in different serological groups but present in the same species. The implication of this site on the possible phylogeny of b-proteins is discussed.Serological tests confirmed the b-protein present as a constitutive component in the virus resistant interspecific hybrids ofN. glutinosa ×N. debneyi as protein b1″.

The detection of PR (b) protein and TMV by ELISA in systemic and localised virus infections of tobacco

An antiserum was prepared to the b1 protein purified from TMV infectedN. tabacum cv. Xanthi-nc leaves and used to study PR proteins. The Xanthi-nc proteins b2 and b3 were shown to be serologically closely related to b1. Antisera to b1 protein and TMV were used in a F(ab')2 enzyme linked immunosorbent assay to monitor PR protein and TMV concentrations, respectively, during the first 6 days of a systemic TMV infection (cv. Xanthi) and a localised TMV infection (cv. Xanthi-nc).

Pathogenesis-related proteins in plants and tissues ofNicotiana tabacum transformed byAgrobacterium tumefaciens

Large amounts of pathogenesis-related (PR) proteins were found inNicotiana tabacum crown gall tissue, following transformation of normal tobacco cells withAgrobacterium tumefaciens. In contrast, PR proteins were not detected in leaves of grafted plants that had been recovered from crown gall tissue even though these plants were still transformed as shown by their inability to form roots and ability to produce octopine. No difference was observed in susceptibility to virus infection between untransformed and transformed plants grafted onto identical rootstocks. The results are discussed in relation to physiological factors controlling PR protein induction and virus resistance.

Specificity of a protein phosphatase inhibitor from rabbit skeletal muscle

A hear-stable protein, which is a specific inhibitor of protein phosphatase-III, was purified 700-fold from skeletal muscle by a procedure that involved heat-treatment at 95 degrees C, chromatography on DEAE-cellulose and gel filtration on Sephadex G-100. The final step completely resolved the protein phosphatase inhibitor from the protein inhibitor of cyclic AMP-dependent protein kinase. The phosphorylase phosphatase, beta-phosphorylase kinase phosphatase, glycogen synthase phosphatase-1 and glycogen synthase phosphatase-2 activities of protein phosphatase-III [Antoniw, J. F., Nimmo, H. G., Yeaman, S. J. & Cohen, P.(1977) Biochem.J. 162, 423-433] were inhibited in a very similar manner by the protein phosphatase inhibitor and at least 95% inhibition was observed at high concentrations of inhibitor. The two forms of protein phosphatase-III, termed IIIA and IIIB, were equally susceptible to the protein phosphatase inhibitor. The protein phosphatase inhibitor was at least 200 times less effective in inhibiting the activity of protein phosphatase-I and protein phosphatase-II. The high degree of specificity of the inhibitor for protein phosphatase-III was used to show that 90% of the phosphorylase phosphatase and glycogen synthase phosphatase activities measured in muscle extracts are catalysed by protein phosphatase-III. Protein phosphatase-III was tightly associated with the protein-glycogen complex that can be isolated from skeletal muscle, whereas the protein phosphatase inhibitor and protein phosphatase-II were not. The results provide further evidence that the enzyme that catalyses the dephosphorylation of the alpha-subunit of phosphorylase kinase (protein phosphatase-II) and the enzyme that catalyses the dephosphorylation of the beta-subunit of phosphorylase kinase (protein phosphatase-III) are distinct. The results suggest that the protein phosphatase inhibitor may be a useful probe for differentiating different classes of protein phosphatases in mammalian cells.

Comparison of the substrate specificities of protein phosphatases involved in the regulation of glycogen metabolism in rabbit skeletal muscle

Muscle extracts were subjected to fractionation with ethanol, chromatography on DEAE-cellulose, precipitation with (NH4)2SO4 and gel filtration on Sephadex G-200. These fractions were assayed for protein phosphatase activities by using the following seven phosphoprotein substrates: phosphorylase a, glycogen synthase b1, glycogen synthase b2, phosphorylase kinase (phosphorylated in either the alpha-subunit or the beta-subunit), histone H1 and histone H2B. Three protein phosphatases with distinctive specificities were resolved by the final gel-filtration step and were termed I, II and III. Protein phosphatase-I, apparent mol.wt. 300000, was an active histone phosphatase, but it accounted for only 10-15% of the glycogen synthase phosphatase-1 and glycogen synthase phosphatase-2 activities and 2-3% of the phosphorylase kinase phosphatase and phosphorylase phosphatase activity recovered from the Sephadex G-200 column. Protein phosphatase-II, apparent mol.wt. 170000, possessed histone phosphatase activity similar to that of protein phosphatase-I. It possessed more than 95% of the activity towards the alpha-subunit of phosphorylase kinase that was recovered from Sephadex G-200. It accounted for 10-15% of the glycogen synthase phosphatase-1 and glycogen synthase phosphatase-2 activity, but less than 5% of the activity against the beta-subunit of phosphorylase kinase and 1-2% of the phosphorylase phosphatase activity recovered from Sephadex G-200. Protein phosphatase-III was the most active histone phosphatase. It possessed 95% of the phosphorylase phosphatase and beta-phosphorylase kinase phosphatase activities, and 75% of the glycogen synthase phosphatase-1 and glycogen synthase phosphatase-2 activities recovered from Sephadex G-200. It accounted for less than 5% of the alpha-phosphorylase kinase phosphatase activity. Protein phosphatase-III was sometimes eluted from Sephadex-G-200 as a species of apparent mol.wt. 75000(termed IIIA), sometimes as a species of mol.wt. 46000(termed IIIB) and sometimes as a mixture of both components. The substrate specificities of protein phosphatases-IIA and -IIB were identical. These findings, taken with the observation that phosphorylase phosphatase, beta-phosphorylase kinase phosphatase, glycogen synthase phosphatase-1 and glycogen synthase phosphatase-2 activities co-purified up to the Sephadex G-200 step, suggest that a single protein phosphatase (protein phosphatase-III) catalyses each of the dephosphorylation reactions that inhibit glycogenolysis or stimulate glycogen synthesis. This contention is further supported by results presented in the following paper [Cohen, P., Nimmo, G.A. & Antoniw, J.F. (1977) Biochem. J. 1628 435-444] which describes a heat-stable protein that is a specific inhibitor of protein phosphatase-III.

Separation of two phosphorylase kinase phosphatases from rabbit skeletal muscle

Cyclic-AMP-dependent protein kinase catalyses the activation of phosphorylase kinase and the phosphorylation of two serine residues on the alpha subunit and beta subunit of phosphorylase kinase [Cohen, P., Watson, D.C. and Dixon, G.H. (1975)]. The dephosphorylation of phosphorylase kinase has been shown to be catalysed by two distinct enzymes, termed alpha-phosphorylase kinase phosphatase and beta-phosphorylase kinase phosphatase. These two enzymes show essentially absolute specificity towards the alpha and beta subunits respectively. The two phosphatases copurified through ethanol fractionation, DEAE-cellulose chromatography and ammonium sulphate precipitation, but were separated from each other by a gel filtration on Sephadex G-200. alpha-Phosphorylase kinase phosphatase was purified 500-fold from the ethanol precipitation step, and beta-phosphorylase kinase phosphatase 320-fold. The molecular weights estimated by gel filtration were 170--180 000 for alpha-phosphorylase kinase phosphatase and 75--80 000 for beta-phosphorylase kinase phosphatase. Since the activity of phosphorylase kinase correlates with the state of phosphorylation of the beta subunit (Cohen, P. (1974)), beta-phosphorylase kinase phosphatase is the enzyme which reverses the activation of phosphorylase kinase. alpha-Phosphorylase kinase phosphatase is an enzyme activity that has not been recognised previously. Since the role of the alpha-subunit phosphorylation is to stimulate the rate of dephosphorylation of the beta subunit (Cohen, P. (1974)), alpha-phosphorylase kinase phosphatase can be regarded as the enzyme which inhibits the reversal of the activation of phosphorylase kinase. The implications of these findings for the hormonal control of phosphorylase kinase activity by multisite phosphorylation are discussed.