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1.
The most comprehensive studies on a plant lysozyme (EC 3.2.1.17) are those on the enzyme from papaya (Carica papaya) latex, published in 1967 and 1969. However, the N-terminal amino acid sequence of five amino acid sequence of this enzyme,
determined by manual Edman degradation, did not allow assignment to any of the much later-classified families of glycosyl
hydrolases. N-Terminal sequence analysis of 22 residues of papaya lysozyme now shows unambiguously that the enzyme belongs
to the family 19 chitinases. It has properties similar to those of basic class I chitinases with lysozyme activity, such as
cleavage specificity at the C-1 of N-acetylmuramic acid with inversion of configuration, but as it lacks an N-terminal hevein domain, it should be classified
as a class II chitinase.
Received: 3 February 1999 / Accepted 25 July 1999 相似文献
2.
Michael Kruse Sally P. Leys Isabel M. Müller Werner E.G. Müller 《Journal of molecular evolution》1998,46(6):721-728
Recent analyses of genes encoding proteins typical for multicellularity, especially adhesion molecules and receptors, favor
the conclusion that all metazoan phyla, including the phylum Porifera (sponges), are of monophyletic origin. However, none
of these data includes cDNA encoding a protein from the sponge class Hexactinellida. We have now isolated and characterized
the cDNA encoding a protein kinase C, belonging to the C subfamily (cPKC), from the hexactinellid sponge Rhabdocalyptus dawsoni. The two conserved regions, the regulatory part with the pseudosubstrate site, the two zinc fingers, and the C2 domain, as
well as the catalytic domain were used for phylogenetic analyses. Sequence alignment and construction of a phylogenetic tree
from the catalytic domains revealed that the yeast Saccharomyces cerevisiae and the protozoan Trypanosoma brucei are at the base of the tree, while the hexactinellid R. dawsoni branches off first among the metazoan sequences; the other two classes of the Porifera, the Calcarea (the sequence from Sycon raphanus was used) and the Demospongiae (sequences from Geodia cydonium and Suberites domuncula were used), branch off later. The statistically robust tree also shows that the two cPKC sequences from the higher invertebrates
Drosophila melanogaster and Lytechinus pictus are most closely related to the calcareous sponge. This finding was also confirmed by comparing the regulatory part of the
kinase gene. We suggest, that (i) within the phylum Porifera, the class Hexactinellida diverged first from a common ancestor
to the Calcarea and the Demospongiae, which both appeared later, and (ii) the higher invertebrates are more closely related
to the calcareous sponges.
Received: 6 August 1997 / Accepted: 24 October 1997 相似文献
3.
Kawase T Saito A Sato T Kanai R Fujii T Nikaidou N Miyashita K Watanabe T 《Applied and environmental microbiology》2004,70(2):1135-1144
In organisms other than higher plants, family 19 chitinase was first discovered in Streptomyces griseus HUT6037, and later, the general occurrence of this enzyme in Streptomyces species was demonstrated. In the present study, the distribution of family 19 chitinases in the class Actinobacteria and the phylogenetic relationship of Actinobacteria family 19 chitinases with family 19 chitinases of other organisms were investigated. Forty-nine strains were chosen to cover almost all the suborders of the class Actinobacteria, and chitinase production was examined. Of the 49 strains, 22 formed cleared zones on agar plates containing colloidal chitin and thus appeared to produce chitinases. These 22 chitinase-positive strains were subjected to Southern hybridization analysis by using a labeled DNA fragment corresponding to the catalytic domain of ChiC, and the presence of genes similar to chiC of S. griseus HUT6037 in at least 13 strains was suggested by the results. PCR amplification and sequencing of the DNA fragments corresponding to the major part of the catalytic domains of the family 19 chitinase genes confirmed the presence of family 19 chitinase genes in these 13 strains. The strains possessing family 19 chitinase genes belong to 6 of the 10 suborders in the order Actinomycetales, which account for the greatest part of the Actinobacteria: Phylogenetic analysis suggested that there is a close evolutionary relationship between family 19 chitinases found in Actinobacteria and plant class IV chitinases. The general occurrence of family 19 chitinase genes in Streptomycineae and the high sequence similarity among the genes found in Actinobacteria suggest that the family 19 chitinase gene was first acquired by an ancestor of the Streptomycineae and spread among the Actinobacteria through horizontal gene transfer. 相似文献
4.
5.
Characterization and Evolution of the Mitochondrial DNA Control Region in Hornbills (Bucerotiformes)
We determined the mitochondrial DNA control region sequences of six Bucerotiformes. Hornbills have the typical avian gene
order and their control region is similar to other avian control regions in that it is partitioned into three domains: two
variable domains that flank a central conserved domain. Two characteristics of the hornbill control region sequence differ
from that of other birds. First, domain I is AT rich as opposed to AC rich, and second, the control region is approximately
500 bp longer than that of other birds. Both these deviations from typical avian control region sequence are explainable on
the basis of repeat motifs in domain I of the hornbill control region. The repeat motifs probably originated from a duplication
of CSB-1 as has been determined in chicken, quail, and snowgoose. Furthermore, the hornbill repeat motifs probably arose before
the divergence of hornbills from each other but after the divergence of hornbills from other avian taxa. The mitochondrial
control region of hornbills is suitable for both phylogenetic and population studies, with domains I and II probably more
suited to population and phylogenetic analyses, respectively. 相似文献
6.
To determine the origin and evolutionary significance of a recently discovered isoform of the estrogen receptor (ERβ), we
examined the phylogenetic relationship of ERβ to the well-known α isoform (ERα) and other steroid receptors. Our phylogenetic
analyses traced the origin of ERβ to a single duplication event at least 450 million years ago. Since this duplication, the
evolution of both ER isoforms has apparently been constrained such that 80% of the amino acid positions in the DNA binding
domain (DBD) and 53% of the ligand binding domain (LBD) have remained unchanged. Using the phylogenetic tree, we determined
the amount of evolutionary change that had occurred in two ER isoforms. The DBD and the LBD had lower rates of evolutionary
change compared to the NH2 terminal domain. However, even with strong selective constraints on the DBD and LBD, our phylogenetic analyses demonstrate
two clearly separate phylogenetic histories for ERα and ERβ dating back several hundred million years. The ancient duplication
of ER and the parallel evolution of the two ER isoforms suggest that, although ERα and ERβ share a substantial degree of sequence
identity, they play unique roles in vertebrate physiology and reproduction.
Received: 19 January 1999 / Accepted: 26 May 1999 相似文献
7.
8.
Evolutionary Relationship of the Ligand-Gated Ion Channels and the Avermectin-Sensitive,Glutamate-Gated Chloride Channels 总被引:4,自引:0,他引:4
Demetrios K. Vassilatis Keith O. Elliston Philip S. Paress Michel Hamelin Joseph P. Arena James M. Schaeffer Lex H.T. Van der Ploeg Doris F. Cully 《Journal of molecular evolution》1997,44(5):501-508
Two cDNAs, GluClα and GluClβ, encoding glutamate-gated chloride channel subunits that represent targets of the avermectin
class of antiparasitic compounds, have recently been cloned from Caenorhabditis elegans (Cully et al., Nature, 371, 707–711, 1994). Expression studies in Xenopus oocytes showed that GluClα and GluClβ have pharmacological profiles distinct from the glutamate-gated cation channels as
well as the γ-aminobutyric acid (GABA)- and glycine-gated chloride channels. Establishing the evolutionary relationship of
related proteins can clarify properties and lead to predictions about their structure and function. We have cloned and determined
the nucleotide sequence of the GluClα and GluClβ genes. In an attempt to understand the evolutionary relationship of these
channels with the members of the ligand-gated ion channel superfamily, we have performed gene structure comparisons and phylogenetic
analyses of their nucleotide and predicted amino acid sequences. Gene structure comparisons reveal the presence of several
intron positions that are not found in the ligand-gated ion channel superfamily, outlining their distinct evolutionary position.
Phylogenetic analyses indicate that GluClα and GluClβ form a monophyletic subbranch in the ligand-gated ion channel superfamily
and are related to vertebrate glycine channels/receptors. Glutamate-gated chloride channels, with electrophysiological properties
similar to GluClα and GluClβ, have been described in insects and crustaceans, suggesting that the glutamate-gated chloride
channel family may be conserved in other invertebrate species. The gene structure and phylogenetic analyses in combination
with the distinct pharmacological properties demonstrate that GluClα and GluClβ belong to a discrete ligand-gated ion channel
family that may represent genes orthologous to the vertebrate glycine channels.
Received: 30 September 1996 / Accepted: 15 November 1996 相似文献
9.
The amino acid sequences of 22 α-amylases from family 13 of glycosyl hydrolases were analyzed with the aim of revealing the
evolutionary relationships between the archaeal α-amylases and their eubacterial and eukaryotic counterparts. Two evolutionary
distance trees were constructed: (i) the first one based on the alignment of extracted best-conserved sequence regions (58
residues) comprising β2, β3, β4, β5, β7, and β8 strand segments of the catalytic (α/β)8-barrel and a short conserved stretch in domain B protruding out of the barrel in the β3 →α3 loop, and (ii) the second one
based on the alignment of the substantial continuous part of the (α/β)8-barrel involving the entire domain B (consensus length: 386 residues). With regard to archaeal α-amylases, both trees compared
brought, in fact, the same results; i.e., all family 13 α-amylases from domain Archaea were clustered with barley pI isozymes,
which represent all plant α-amylases. The enzymes from Bacillus licheniformis and Escherichia coli, representing liquefying and cytoplasmic α-amylases, respectively, seem to be the further closest relatives to archaeal α-amylases.
This evolutionary relatedness clearly reflects the discussed similarities in the amino acid sequences of these α-amylases,
especially in the best-conserved sequence regions. Since the results for α-amylases belonging to all three domains (Eucarya,
Eubacteria, Archaea) offered by both evolutionary trees are very similar, it is proposed that the investigated conserved sequence
regions may indeed constitute the ``sequence fingerprints' of a given α-amylase.
Received: 3 June 1998 / Accepted: 20 August 1998 相似文献
10.
The members of the PKA regulatory subunit family (PKA-R family) were analyzed by multiple sequence alignment and clustering
based on phylogenetic tree construction. According to the phylogenetic trees generated from multiple sequence alignment of
the complete sequences, the PKA-R family was divided into four subfamilies (types I to IV). Members of each subfamily were
exclusively from animals (types I and II), fungi (type III), and alveolates (type IV). Application of the same methodology
to the cAMP-binding domains, and subsequently to the region delimited by β-strands 6 and 7 of the crystal structures of bovine
RIα and rat RIIβ (the phosphate-binding cassette; PBC), proved that this highly conserved region was enough to classify unequivocally
the members of the PKA-R family. A single signature sequence, F–G–E–[LIV]–A–L–[LIMV]–x(3)–[PV]–R–[ANQV]–A, corresponding to
the PBC was identified which is characteristic of the PKA-R family and is sufficient to distinguish it from other members
of the cyclic nucleotide-binding protein superfamily. Specific determinants for the A and B domains of each R-subunit type
were also identified. Conserved residues defining the signature motif are important for interaction with cAMP or for positioning
the residues that directly interact with cAMP. Conversely, residues that define subfamilies or domain types are not conserved
and are mostly located on the loop that connects α-helix B′ and β strand 7.
Received: 2 November 2000/Accepted: 14 June 2001 相似文献
11.
Molecular evolution of nitrate reductase genes 总被引:9,自引:0,他引:9
To understand the evolutionary mechanisms and relationships of nitrate reductases (NRs), the nucleotide sequences encoding
19 nitrate reductase (NR) genes from 16 species of fungi, algae, and higher plants were analyzed. The NR genes examined show
substantial sequence similarity, particularly within functional domains, and large variations in GC content at the third codon
position and intron number. The intron positions were different between the fungi and plants, but conserved within these groups.
The overall and nonsynonymous substitution rates among fungi, algae, and higher plants were estimated to be 4.33 × 10−10 and 3.29 × 10−10 substitutions per site per year. The three functional domains of NR genes evolved at about one-third of the rate of the N-terminal
and the two hinge regions connecting the functional domains. Relative rate tests suggested that the nonsynonymous substitution
rates were constant among different lineages, while the overall nucleotide substitution rates varied between some lineages.
The phylogenetic trees based on NR genes correspond well with the phylogeny of the organisms determined from systematics and
other molecular studies. Based on the nonsynonymous substitution rate, the divergence time of monocots and dicots was estimated
to be about 340 Myr when the fungi–plant or algae–higher plant divergence times were used as reference points and 191 Myr
when the rice–barley divergence time was used as a reference point. These two estimates are consistent with other estimates
of divergence times based on these reference points. The lack of consistency between these two values appears to be due to
the uncertainty of the reference times.
Received: 10 April 1995 / Accepted: 10 September 1995 相似文献
12.
Piero Cammarano Roberta Creti Anna M. Sanangelantoni Peter Palm 《Journal of molecular evolution》1999,49(4):524-537
A global alignment of EF-G(2) sequences was corrected by reference to protein structure. The selection of characters eligible
for construction of phylogenetic trees was optimized by searching for regions arising from the artifactual matching of sequence
segments unique to different phylogenetic domains. The spurious matchings were identified by comparing all sections of the
global alignment with a comprehensive inventory of significant binary alignments obtained by BLAST probing of the DNA and
protein databases with representative EF-G(2) sequences. In three discrete alignment blocks (one in domain II and two in domain
IV), the alignment of the bacterial sequences with those of Archaea–Eucarya was not retrieved by database probing with EF-G(2)
sequences, and no EF-G homologue of the EF-2 sequence segments was detected by using partial EF-G(2) sequences as probes in
BLAST/FASTA searches. The two domain IV regions (one of which comprises the ADP-ribosylatable site of EF-2) are almost certainly
due to the artifactual alignment of insertion segments that are unique to Bacteria and to Archaea–Eucarya. Phylogenetic trees
have been constructed from the global alignment after deselecting positions encompassing the unretrieved, spuriously aligned
regions, as well as positions arising from misalignment of the G′ and G″ subdomain insertion segments flanking the ``fifth'
consensus motif of the G domain (?varsson, 1995). The results show inconsistencies between trees inferred by alternative methods
and alternative (DNA and protein) data sets with regard to Archaea being a monophyletic or paraphyletic grouping. Both maximum-likelihood
and maximum-parsimony methods do not allow discrimination (by log-likelihood difference and difference in number of inferred
substitutions) between the conflicting (monophyletic vs. paraphyletic Archaea) topologies. No specific EF-2 insertions (or
terminal accretions) supporting a crenarchaeal–eucaryal clade are detectable in the new EF-G(2) sequence alignment. 相似文献
13.
Purification of two chitinases from Rhizopus oligosporus and isolation and sequencing of the encoding genes.
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K Yanai N Takaya N Kojima H Horiuchi A Ohta M Takagi 《Journal of bacteriology》1992,174(22):7398-7406
Two chitinases were purified from Rhizopus oligosporus, a filamentous fungus belonging to the class Zygomycetes, and designated chitinase I and chitinase II. Their N-terminal amino acid sequences were determined, and two synthetic oligonucleotide probes corresponding to these amino acid sequences were synthesized. Southern blot analyses of the total genomic DNA from R. oligosporus with these oligonucleotides as probes indicated that one of the two genes encoding these two chitinases was contained in a 2.9-kb EcoRI fragment and in a 3.6-kb HindIII fragment and that the other one was contained in a 2.9-kb EcoRI fragment and in a 11.5-kb HindIII fragment. Two DNA fragments were isolated from the phage bank of R. oligosporus genomic DNA with the synthetic oligonucleotides as probes. The restriction enzyme analyses of these fragments coincided with the Southern blot analyses described above and the amino acid sequences deduced from their nucleotide sequences contained those identical to the determined N-terminal amino acid sequences of the purified chitinases, indicating that each of these fragments contained a gene encoding chitinase (designated chi 1 and chi 2, encoding chitinase I and II, respectively). The deduced amino acid sequences of these two genes had domain structures similar to that of the published sequence of chitinase of Saccharomyces cerevisiae, except that they had an additional C-terminal domain. Furthermore, there were significant differences between the molecular weights experimentally determined with the two purified enzymes and those deduced from the nucleotide sequences for both genes. Analysis of the N- and C-terminal amino acid sequences of both chitinases and comparison of them with the amino acid sequences deduced from the nucleotide sequences revealed posttranslational processing not only at the N-terminal signal sequences but also at the C-terminal domains. It is concluded that these chitinases are synthesized with pre- and prosequences in addition to the mature enzyme sequences and that the prosequences are located at the C terminal. 相似文献
14.
Bacterial family C DNA polymerases (DNA pol IIIs), the major chromosomal replicative enzymes, have been provisionally classified
based on primary sequences and domain structures into three classes: class I (Escherichia coli DNA pol C-type), class II (Bacillus subtilis DNA pol C-type), and class III (cyanobacterial DNA pol C-type), respectively. We have sequenced the structural gene encoding
the DNA pol C catalytic subunit of the thermophilic bacterium Thermus aquaticus. This gene, designated the Taq DNA pol C gene, contains a 3660-bp open reading frame which specifies a polypeptide of molecular
weight of 137,388 daltons. Comparative sequence analyses revealed that Taq DNA pol C is a class I family C DNA polymerase.
The Taq DNA pol C is most closely related to the Deinococcus radiodurans DNA pol C. Although a phylogenetic tree based on the class I family C DNA pols is still in the provisional stage, some important
conclusion can be drawn. First, the high-G+C and the low-G+C Gram-positive bacteria are not monophyletic. Second, the low-G+C
Gram-positive bacteria contain multigenes of family C DNA pols (classes I and II). Third, the cyanobacterial family C DNA
pol, classified as class III because it is encoded by a split gene, forms a group with the high-G+C Gram-positive bacteria.
Received: 7 October 1998 / Accepted: 12 January 1999 相似文献
15.
Sarma K Dehury B Sahu J Sarmah R Sahoo S Sahu M Sen P Modi MK Barooah M 《Journal of molecular modeling》2012,18(11):4761-4780
Glycoside hydrolase family 19 chitinases (EC 3.2.1.14) widely distributed in plants, bacteria and viruses catalyse the hydrolysis of chitin and play a major role in plant defense mechanisms and development. Rice possesses several classes of chitinase, out of which a single structure of class I has been reported in PDB to date. In the present study an attempt was made to gain more insight into the structure, function and evolution of class I, II and IV chitinases of GH family 19 from rice. The three-dimensional structures of chitinases were modelled and validated based on available X-ray crystal structures. The structural study revealed that they are highly α-helical and bilobed in nature. These enzymes are single or multi domain and multi-functional in which chitin-binding domain (CBD) and catalytic domain (CatD) are present in class I and IV whereas class II lacks CBD. The CatD possesses a catalytic triad which is thought to be involved in catalytic process. Loop III, which is common in all three classes of chitinases, reflects that it may play a significant role in their function. Our study also confirms that the absence and presence of different loops in GH family 19 of rice may be responsible for various sized products. Molecular phylogeny revealed chitinases in monocotyledons and dicotyledons differed from each other forming two different clusters and may have evolved differentially. More structural study of this enzyme from different plants is required to enhance the knowledge of catalytic mechanism and substrate binding. 相似文献
16.
Michael Kruse Vera Gamulin Helena Cetkovic Zeev Pancer Isabel M. Müller Werner E. G. Müller 《Journal of molecular evolution》1996,43(4):374-383
Protein kinases C (PKCs) comprise closely related Ser/Thr kinases, ubiquitously present in animal tissues; they respond to
second messengers, e.g., Ca2+ and/or diacylglycerol, to express their activities. Two PKCs have been sequenced from Geodia cydonium, a member of the lowest multicellular animals, the sponges (Porifera). One sponge G. cydonium PKC, GCPKC1, belongs to the ``novel' (Ca2+-independent) PKC (nPKC) subfamily while the second one, GCPKC2, has the hallmarks of the ``conventional' (Ca2+-dependent) PKC (cPKC) subfamily. The alignment of the Ser/Thr catalytic kinase domains, of the predicted aa sequences for
these cDNAs with respective segments from previously reported sequences, revealed highest homology to PKCs from animals but
also distant relationships to Ser/Thr kinases from protozoa, plants, and bacteria. However, a comparison of the complete structures
of the sponge PKCs, which are—already—identical to those of nPKCs and cPKCs from higher metazoa, with the structures of protozoan,
plant, and bacterial Ser/Thr kinases indicates that the metazoan PKCs have to be distinguished from the nonmetazoan enzymes.
These data indicate that metazoan PKCs have a universal common ancestor which they share with the nonmetazoan Ser/Thr kinases
with respect to the kinase domain, but they differ from them in overall structural composition.
Received: 10 January 1996 / Accepted: 12 March 1996 相似文献
17.
Colm O'hUigin Holger Sültmann Herbert Tichy Brent W. Murray 《Journal of molecular evolution》1998,47(5):578-585
We report the cDNA sequences for the DMA and DMB family of Mhc genes of the gray short-tailed opossum. Until now DM sequences were available only in eutherian mammals. The marsupial sequences indicate that both members of the family are
old and probably diverged from other classical class II families about the time of the radiation of jawed vertebrates some
450 million years ago. We examine the evolutionary rates of equivalent sets of classical and nonclassical genes to check for
rate heterogeneity. We find the α-1 domain of the DR genes to be untypically conservative in its evolutionary mode. The DM genes appear to evolve at rates typical of other class II genes, indicating that their placement at the root of class II
gene evolutionary trees may be justified.
Received: 2 March 1998 / Accepted: 2 June 1998 相似文献
18.
Bernard Labedan Anne Boyen Margot Baetens Daniel Charlier Pingguo Chen Raymond Cunin Virginie Durbeco Nicolas Glansdorff Guy Herve Christianne Legrain Ziyuan Liang Christina Purcarea Martine Roovers Rony Sanchez Thia-Lin Toong Marc Van de Casteele Françoise van Vliet Ying Xu Yuan-Fu Zhang 《Journal of molecular evolution》1999,49(4):461-473
Forty-four sequences of ornithine carbamoyltransferases (OTCases) and 33 sequences of aspartate carbamoyltransferases (ATCases)
representing the three domains of life were multiply aligned and a phylogenetic tree was inferred from this multiple alignment.
The global topology of the composite rooted tree (each enzyme family being used as an outgroup to root the other one) suggests
that present-day genes are derived from paralogous ancestral genes which were already of the same size and argues against
a mechanism of fusion of independent modules. A closer observation of the detailed topology shows that this tree could not
be used to assess the actual order of organismal descent. Indeed, this tree displays a complex topology for many prokaryotic
sequences, with polyphyly for Bacteria in both enzyme trees and for the Archaea in the OTCase tree. Moreover, representatives
of the two prokaryotic Domains are found to be interspersed in various combinations in both enzyme trees. This complexity
may be explained by assuming the occurrence of two subfamilies in the OTCase tree (OTC α and OTC β) and two other ones in
the ATCase tree (ATC I and ATC II). These subfamilies could have arisen from duplication and selective losses of some differentiated
copies during the successive speciations. We suggest that Archaea and Eukaryotes share a common ancestor in which the ancestral
copies giving the present-day ATC II/OTC β combinations were present, whereas Bacteria comprise two classes: one containing
the ATC II/OTC α combination and the other harboring the ATC I/OTC β combination. Moreover, multiple horizontal gene transfers
could have occurred rather recently amongst prokaryotes. Whichever the actual history of carbamoyltransferases, our data suggest
that the last common ancestor to all extant life possessed differentiated copies of genes coding for both carbamoyltransferases,
indicating it as a rather sophisticated organism. 相似文献
19.
Evolution of Chitin-Binding Proteins in Invertebrates 总被引:11,自引:0,他引:11
Analysis of a group of invertebrate proteins, including chitinases and peritrophic matrix proteins, reveals the presence
of chitin-binding domains that share significant amino acid sequence similarity. The data suggest that these domains evolved
from a common ancestor which may be a protein containing a single chitin-binding domain. The duplication and transposition
of this chitin-binding domain may have contributed to the functional diversification of chitin-binding proteins. Sequence
comparisons indicated that invertebrate and plant chitin binding domains do not share significant amino acid sequence similarity,
suggesting that they are not coancestral. However, both the invertebrate and the plant chitin-binding domains are cysteine-rich
and have several highly conserved aromatic residues. In plants, cysteines have been elucidated in maintaining protein folding
and aromatic amino acids in interacting with saccharides [Wright HT, Sanddrasegaram G, Wright CS (1991) J Mol Evol 33:283–294].
It is likely that these residues perform similar functions in invertebrates. We propose that the invertebrate and the plant
chitin-binding domains share similar mechanisms for folding and saccharide binding and that they evolved by convergent evolution.
Furthermore, we propose that the disulfide bonds and aromatic residues are hallmarks for saccharide-binding proteins.
Received: 2 March 1998 / Accepted: 17 July 1998 相似文献
20.
Various chitinases have been identified in plants and categorized into several groups based on the analysis of their sequences
and domains. We have isolated a tobacco gene that encodes a predicted polypeptide consisting of a 20-amino acid N-terminal
signal peptide, followed by a 245-amino acid chitinolytic domain. Although the predicted mature protein is basic and shows
greater sequence identity to basic class I chitinases (75%) than to acidic class II chitinases (67%), it lacks the N-terminal
cysteine-rich domain and the C-terminal vacuolar targeting signal that is diagnostic for class I chitinases. Therefore, this
gene appears to encode a novel, basic, class II chitinase, which we have designated NtChia2;B1. Accumulation of Chia2;B1 mRNA was induced in leaves in association with the local-lesion response to tobacco mosaic virus (TMV) infection, and in
response to treatment with salicylic acid, but was only slightly induced by treatment with ethephon. Little or no Chia2;B1 mRNA was detected in roots, flowers, and cell-suspension cultures, in which class I chitinase mRNAs accumulate to high concentrations.
Sequence comparisons of Chia2;B1 with known tobacco class I and class II chitinase genes suggest that Chia2;B1 might encode an ancestral prototype of the present-day class I and class II isoforms. Possible mechanisms for chitinase gene
evolution are discussed.
Received: 25 May 1998 / Accepted: 29 June 1998 相似文献