Spontaneous assembly of a self-complementary oligopeptide to form a stable macroscopic membrane

A 16-residue peptide [(Ala-Glu-Ala-Glu-Ala-Lys-Ala-Lys)2] has a characteristic beta-sheet circular dichroism spectrum in water. Upon the addition of salt, the peptide spontaneously assembles to form a macroscopic membrane. The membrane does not dissolve in heat or in acidic or alkaline solutions, nor does it dissolve upon addition of guanidine hydrochloride, SDS/urea, or a variety of proteolytic enzymes. Scanning EM reveals a network of interwoven filaments approximately 10-20 nm in diameter. An important component of the stability is probably due to formation of complementary ionic bonds between glutamic and lysine side chains. This phenomenon may be a model for studying the insoluble peptides found in certain neurological disorders. It may also have implications for biomaterials and origin-of-life research.

Single-nucleotide polymorphism in the human mu opioid receptor gene alters beta-endorphin binding and activity: possible implications for opiate addiction

Opioid drugs play important roles in the clinical management of pain, as well as in the development and treatment of drug abuse. The mu opioid receptor is the primary site of action for the most commonly used opioids, including morphine, heroin, fentanyl, and methadone. By sequencing DNA from 113 former heroin addicts in methadone maintenance and 39 individuals with no history of drug or alcohol abuse or dependence, we have identified five different single-nucleotide polymorphisms (SNPs) in the coding region of the mu opioid receptor gene. The most prevalent SNP is a nucleotide substitution at position 118 (A118G), predicting an amino acid change at a putative N-glycosylation site. This SNP displays an allelic frequency of approximately 10% in our study population. Significant differences in allele distribution were observed among ethnic groups studied. The variant receptor resulting from the A118G SNP did not show altered binding affinities for most opioid peptides and alkaloids tested. However, the A118G variant receptor binds beta-endorphin, an endogenous opioid that activates the mu opioid receptor, approximately three times more tightly than the most common allelic form of the receptor. Furthermore, beta-endorphin is approximately three times more potent at the A118G variant receptor than at the most common allelic form in agonist-induced activation of G protein-coupled potassium channels. These results show that SNPs in the mu opioid receptor gene can alter binding and signal transduction in the resulting receptor and may have implications for normal physiology, therapeutics, and vulnerability to develop or protection from diverse diseases including the addictive diseases.

Extensive neurite outgrowth and active synapse formation on self-assembling peptide scaffolds

A new type of self-assembling peptide (sapeptide) scaffolds that serve as substrates for neurite outgrowth and synapse formation is described. These peptide-based scaffolds are amenable to molecular design by using chemical or biotechnological syntheses. They can be tailored to a variety of applications. The sapeptide scaffolds are formed through the spontaneous assembly of ionic self-complementary beta-sheet oligopeptides under physiological conditions, producing a hydrogel material. The scaffolds can support neuronal cell attachment and differentiation as well as extensive neurite outgrowth. Furthermore, they are permissive substrates for functional synapse formation between the attached neurons. That primary rat neurons form active synapses on such scaffold surfaces in situ suggests these scaffolds could be useful for tissue engineering applications. The buoyant sapeptide scaffolds with attached cells in culture can be transported readily from one environment to another. Furthermore, these peptides did not elicit a measurable immune response or tissue inflammation when introduced into animals. These biological materials created through molecular design and self assembly may be developed as a biologically compatible scaffold for tissue repair and tissue engineering.

Self-assembling peptide hydrogel fosters chondrocyte extracellular matrix production and cell division: implications for cartilage tissue repair

Emerging medical technologies for effective and lasting repair of articular cartilage include delivery of cells or cell-seeded scaffolds to a defect site to initiate de novo tissue regeneration. Biocompatible scaffolds assist in providing a template for cell distribution and extracellular matrix (ECM) accumulation in a three-dimensional geometry. A major challenge in choosing an appropriate scaffold for cartilage repair is the identification of a material that can simultaneously stimulate high rates of cell division and high rates of cell synthesis of phenotypically specific ECM macromolecules until repair evolves into steady-state tissue maintenance. We have devised a self-assembling peptide hydrogel scaffold for cartilage repair and developed a method to encapsulate chondrocytes within the peptide hydrogel. During 4 weeks of culture in vitro, chondrocytes seeded within the peptide hydrogel retained their morphology and developed a cartilage-like ECM rich in proteoglycans and type II collagen, indicative of a stable chondrocyte phenotype. Time-dependent accumulation of this ECM was paralleled by increases in material stiffness, indicative of deposition of mechanically functional neo-tissue. Taken together, these results demonstrate the potential of a self-assembling peptide hydrogel as a scaffold for the synthesis and accumulation of a true cartilage-like ECM within a three-dimensional cell culture for cartilage tissue repair.

Rho family GTPases regulate p38 mitogen-activated protein kinase through the downstream mediator Pak1

The stress-activated p38 mitogen-activated protein (MAP) kinase defines a subgroup of the mammalian MAP kinases that appear to play a key role in regulating inflammatory responses. Co-expression of constitutively active forms of Rac and Cdc42 leads to activation of p38 while dominant negative Rac and Cdc42 inhibit the ability of interleukin-1 to increase p38 activity. p21-activated kinase 1 (Pak1) is a potential mediator of Rac/Cdc42 signaling, and we observe that Pak1 stimulates p38 activity. A dominant negative Pak1 suppresses both interleukin-1- and Rac/Cdc42-induced p38 activity. Rac and Cdc42 appear to regulate a protein kinase cascade initiated at the level of Pak and leading to activation of p38 and JNK.

The genome of the natural genetic engineer Agrobacterium tumefaciens C58

The 5.67-megabase genome of the plant pathogen Agrobacterium tumefaciens C58 consists of a circular chromosome, a linear chromosome, and two plasmids. Extensive orthology and nucleotide colinearity between the genomes of A. tumefaciens and the plant symbiont Sinorhizobium meliloti suggest a recent evolutionary divergence. Their similarities include metabolic, transport, and regulatory systems that promote survival in the highly competitive rhizosphere; differences are apparent in their genome structure and virulence gene complement. Availability of the A. tumefaciens sequence will facilitate investigations into the molecular basis of pathogenesis and the evolutionary divergence of pathogenic and symbiotic lifestyles.

Identifying tumor suppressors in genetic mosaics: the Drosophila lats gene encodes a putative protein kinase

We have identified recessive overproliferation mutations by screening and examining clones of mutant cells in genetic mosaics of the fruitfly Drosophila melanogaster. This type of screen provides a powerful approach for identifying and studying potential tumor suppressors. One of the identified genes, lats, has been cloned and encodes a putative protein kinase that shares high levels of sequence similarity with three proteins in budding yeast and Neurospora that are involved in regulation of the cell cycle and growth. Mutations in lats cause dramatic overproliferation phenotypes and various developmental defects in both mosaic animals and homozygous mutants.

Prospective study of body mass index, weight change, and risk of adult-onset asthma in women

BACKGROUND

Obesity and asthma are common disorders, and their prevalence rates continue to rise. Although individuals with asthma may gain weight as a result of activity limitations, the relationship between body mass index (BMI), which is calculated as weight in kilograms divided by the square of height in meters, and risk of developing asthma is not known.

METHODS

We performed a prospective cohort study of female US registered nurses in the Nurses' Health Study II. In 1991, after excluding women who died with probable asthma or with incomplete data, there were 85911 participants, aged 26 to 46 years. The main outcome measure was self-report of physician-diagnosed asthma with recent use of an asthma medication.

RESULTS

From 1991 to 1995, we identified 1596 incident cases of asthma. In a multivariate model controlling for 9 potential confounding factors (including age, race, smoking, physical activity, and energy intake), the relative risks of asthma for 6 increasing categories of BMI in 1991 were 0.9, 1.0 (reference), 1.1, 1.6, 1.7, and 2.7 (P for trend <.001). Stronger associations were found using stricter definitions for asthma, and the finding was present in a variety of subgroups. In analyses controlling for the same variables, as well as BMI at age 18, women who gained weight after age 18 were at significantly increased risk of developing asthma during the 4-year follow-up period (P for trend <.001).

CONCLUSIONS

The BMI has a strong, independent, and positive association with risk of adult-onset asthma. The increasing prevalence of obesity in developed nations may help explain concomitant increases in asthma prevalence.

Exosomes derived from human embryonic mesenchymal stem cells promote osteochondral regeneration

OBJECTIVE

Clinical and animal studies have demonstrated the efficacy of mesenchymal stem cell (MSC) therapies in cartilage repair. As the efficacy of many MSC-based therapies has been attributed to paracrine secretion, particularly extracellular vesicles/exosomes, we determine here if weekly intra-articular injections of human embryonic MSC-derived exosomes would repair and regenerate osteochondral defects in a rat model.

METHODS

In this study, osteochondral defects were created on the trochlear grooves of both distal femurs in 12 adult rats. In each animal, one defect was treated with 100 μg exosomes and the contralateral defect treated with phosphate buffered saline (PBS). Intra-articular injections of exosomes or PBS were administered after surgery and thereafter weekly for a period of 12 weeks. Three unoperated age-matched animals served as native controls. Analyses were performed by histology, immunohistochemistry, and scoring at 6 and 12 weeks after surgery.

RESULTS

Generally, exosome-treated defects showed enhanced gross appearance and improved histological scores than the contralateral PBS-treated defects. By 12 weeks, exosome-treated defects displayed complete restoration of cartilage and subchondral bone with characteristic features including a hyaline cartilage with good surface regularity, complete bonding to adjacent cartilage, and extracellular matrix deposition that closely resemble that of age-matched unoperated control. In contrast, there were only fibrous repair tissues found in the contralateral PBS-treated defects.

CONCLUSION

This study demonstrates for the first time the efficacy of human embryonic MSC exosomes in cartilage repair, and the utility of MSC exosomes as a ready-to-use and 'cell-free' therapeutic alternative to cell-based MSC therapy.

The Biomolecular Interaction Network Database and related tools 2005 update

The Biomolecular Interaction Network Database (BIND) (http://bind.ca) archives biomolecular interaction, reaction, complex and pathway information. Our aim is to curate the details about molecular interactions that arise from published experimental research and to provide this information, as well as tools to enable data analysis, freely to researchers worldwide. BIND data are curated into a comprehensive machine-readable archive of computable information and provides users with methods to discover interactions and molecular mechanisms. BIND has worked to develop new methods for visualization that amplify the underlying annotation of genes and proteins to facilitate the study of molecular interaction networks. BIND has maintained an open database policy since its inception in 1999. Data growth has proceeded at a tremendous rate, approaching over 100 000 records. New services provided include a new BIND Query and Submission interface, a Standard Object Access Protocol service and the Small Molecule Interaction Database (http://smid.blueprint.org) that allows users to determine probable small molecule binding sites of new sequences and examine conserved binding residues.

Self-complementary oligopeptide matrices support mammalian cell attachment

A new class of ionic self-complementary oligopeptides is described, two members of which have been designated RAD16 and EAK16. These oligopeptides consist of regular repeats of alternating ionic hydrophilic and hydrophobic amino acids and associate to form stable beta-sheet structures in water. The addition of buffers containing millimolar amounts of monovalent salts or the transfer of a peptide solution into physiological solutions results in the spontaneous assembly of the oligopeptides into a stable, macroscopic membranous matrix. The matrix is composed of ordered filaments which form porous enclosures. A variety of mammalian cell types are able to attach to both RAD16 and EAK16 membranous matrices. These matrices provide a novel experimental system for analysing mechanisms of in vitro cell attachment and may have applications in in vivo studies of tissue regeneration, tissue transplantation and would healing.

MAPK cascades in plant defense signaling

The Arabidopsis genome encodes approximately 20 different mitogen-activated protein kinases (MAPKs) that are likely to be involved in growth, development and responses to endogenous and environmental cues. Several plant MAPKs are activated by a variety of stress stimuli, including pathogen infection, wounding, temperature, drought, salinity, osmolarity, UV irradiation, ozone and reactive oxygen species. Recent gain-of-function studies show that two tobacco MAPKs induce the expression of defense genes and cause cell death. By contrast, loss-of-function studies of other MAPK pathways revealed negative regulation of disease resistance. This 'push-and-pull' regulation by different MAPK pathways might provide a more precise control of plant defense responses.

Inactivation of NMDA receptors by direct interaction of calmodulin with the NR1 subunit

NMDA (N-methyl-D-aspartate) receptors are excitatory neurotransmitter receptors in the brain critical for synaptic plasticity and neuronal development. These receptors are Ca2+-permeable glutamate-gated ion channels whose physiological properties are regulated by intracellular Ca2+. We report here the purification of a 20 kDa protein identified as calmodulin that interacts with the NR1 subunit of the NMDA receptor. Calmodulin binding to the NR1 subunit is Ca2+ dependent and occurs with homomeric NR1 complexes, heteromeric NR1/NR2 subunit complexes, and NMDA receptors from brain. Furthermore, calmodulin binding to NR1 causes a 4-fold reduction in NMDA channel open probability. These results demonstrate that NMDA receptor function can be regulated by direct binding of calmodulin to the NR1 subunit, and suggest a possible mechanism for activity-dependent feedback inhibition and Ca2+-dependent inactivation of NMDA receptors.

Pan-Asian adapted ESMO consensus guidelines for the management of patients with metastatic colorectal cancer: a JSMO-ESMO initiative endorsed by CSCO, KACO, MOS, SSO and TOS

The most recent version of the European Society for Medical Oncology (ESMO) consensus guidelines for the treatment of patients with metastatic colorectal cancer (mCRC) was published in 2016, identifying both a more strategic approach to the administration of the available systemic therapy choices, and a greater emphasis on the use of ablative techniques, including surgery. At the 2016 ESMO Asia Meeting, in December 2016, it was decided by both ESMO and the Japanese Society of Medical Oncology (JSMO) to convene a special guidelines meeting, endorsed by both ESMO and JSMO, immediately after the JSMO 2017 Annual Meeting. The aim was to adapt the ESMO consensus guidelines to take into account the ethnic differences relating to the toxicity as well as other aspects of certain systemic treatments in patients of Asian ethnicity. These guidelines represent the consensus opinions reached by experts in the treatment of patients with mCRC identified by the Presidents of the oncological societies of Japan (JSMO), China (Chinese Society of Clinical Oncology), Korea (Korean Association for Clinical Oncology), Malaysia (Malaysian Oncological Society), Singapore (Singapore Society of Oncology) and Taiwan (Taiwan Oncology Society). The voting was based on scientific evidence and was independent of both the current treatment practices and the drug availability and reimbursement situations in the individual participating Asian countries.

Neurotransplantation of magnetically labeled oligodendrocyte progenitors: magnetic resonance tracking of cell migration and myelination

Demyelination is a common pathological finding in human neurological diseases and frequently persists as a result of failure of endogenous repair. Transplanted oligodendrocytes and their precursor cells can (re)myelinate axons, raising the possibility of therapeutic intervention. The migratory capacity of transplanted cells is of key importance in determining the extent of (re)myelination and can, at present, be evaluated only by using invasive and irreversible procedures. We have exploited the transferrin receptor as an efficient intracellular delivery device for magnetic nanoparticles, and transplanted tagged oligodendrocyte progenitor cells into the spinal cord of myelin-deficient rats. Cell migration could be easily detected by using three-dimensional magnetic resonance microscopy, with a close correlation between the areas of contrast enhancement and the achieved extent of myelination. The present results demonstrate that magnetic resonance tracking of transplanted oligodendrocyte progenitors is feasible; this technique has the potential to be easily extended to other neurotransplantation studies involving different precursor cell types.

Nitric oxide and salicylic acid signaling in plant defense

Salicylic acid (SA) plays a critical signaling role in the activation of plant defense responses after pathogen attack. We have identified several potential components of the SA signaling pathway, including (i) the H(2)O(2)-scavenging enzymes catalase and ascorbate peroxidase, (ii) a high affinity SA-binding protein (SABP2), (iii) a SA-inducible protein kinase (SIPK), (iv) NPR1, an ankyrin repeat-containing protein that exhibits limited homology to IkappaBalpha and is required for SA signaling, and (v) members of the TGA/OBF family of bZIP transcription factors. These bZIP factors physically interact with NPR1 and bind the SA-responsive element in promoters of several defense genes, such as the pathogenesis-related 1 gene (PR-1). Recent studies have demonstrated that nitric oxide (NO) is another signal that activates defense responses after pathogen attack. NO has been shown to play a critical role in the activation of innate immune and inflammatory responses in animals. Increases in NO synthase (NOS)-like activity occurred in resistant but not susceptible tobacco after infection with tobacco mosaic virus. Here we demonstrate that this increase in activity participates in PR-1 gene induction. Two signaling molecules, cGMP and cyclic ADP ribose (cADPR), which function downstream of NO in animals, also appear to mediate plant defense gene activation (e.g., PR-1). Additionally, NO may activate PR-1 expression via an NO-dependent, cADPR-independent pathway. Several targets of NO in animals, including guanylate cyclase, aconitase, and mitogen-activated protein kinases (e.g., SIPK), are also modulated by NO in plants. Thus, at least portions of NO signaling pathways appear to be shared between plants and animals.

Final overall survival results from a randomised, phase III study of erlotinib versus chemotherapy as first-line treatment of EGFR mutation-positive advanced non-small-cell lung cancer (OPTIMAL, CTONG-0802)

BACKGROUND

The OPTIMAL study was the first study to compare efficacy and tolerability of the epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) erlotinib, versus standard chemotherapy in first-line treatment of patients with EGFR mutation-positive advanced non-small-cell lung cancer (NSCLC). Findings from final overall survival (OS) analysis and assessment of post-study treatment impact are presented.

PATIENTS AND METHODS

Of 165 randomised patients, 82 received erlotinib and 72 gemcitabine plus carboplatin. Final OS analyses were conducted when 70% of deaths had occurred in the intent-to-treat population. Subgroup OS was analysed by Cox proportional hazards model and included randomisation stratification factors and post-study treatments.

RESULTS

Median OS was similar between the erlotinib (22.8 months) and chemotherapy (27.2 months) arms with no significant between-group differences in the overall population [hazard ratio (HR), 1.19; 95% confidence interval (CI) 0.83-1.71; P = 0.2663], the exon 19 deletion subpopulation (HR, 1.52; 95% CI 0.91-2.52; P = 0.1037) or the exon 21 L858 mutation subpopulation (HR, 0.92; 95% CI 0.55-1.54; P = 0.7392). More patients in the erlotinib arm versus the chemotherapy arm did not receive any post-study treatment (36.6% versus 22.2%). Patients who received sequential combination of EGFR-TKI and chemotherapy had significantly improved OS compared with those who received EGFR-TKI or chemotherapy only (29.7 versus 20.7 or 11.2 months, respectively; P < 0.0001). OS was significantly shorter in patients who did not receive post-study treatments compared with those who received subsequent treatments in both arms.

CONCLUSION

The significant OS benefit observed in patients treated with EGFR-TKI emphasises its contribution to improving survival of EGFR mutant NSCLC patients, suggesting that erlotinib should be considered standard first-line treatment of EGFR mutant patients and EGFR-TKI treatment following first-line therapy also brings significant benefits to those patients.

CLINICALTRIALSGOV IDENTIFIER

NCT00874419.

Desensitization of AMPA receptors upon multiquantal neurotransmitter release

We have investigated the role of AMPA receptor desensitization during transmission at a calyceal synapse. Cyclothiazide blocked the rapid desensitization of AMPA receptors and markedly prolonged the decay time of the evoked excitatory postsynaptic current (PSC). This effect was greater than what would be expected from a simple prolongation of channel open time. Additionally, the drug reduced the depression of PSCs evoked at brief intervals. The effects of cyclothiazide on the PSC were reduced when the level of transmitter release was lowered. These data indicate that AMPA receptors are desensitized by neurotransmitter and that this desensitization depends on the number of quanta in the synaptic cleft. We propose that release of transmitter from many closely spaced sites prolongs the time of receptor-transmitter contact and thereby promotes desensitization. Desensitization may therefore contribute to synaptic depression and prevent the interaction of transmitter quanta within the synaptic cleft.

Generation of cancer stem-like cells through the formation of polyploid giant cancer cells

Polyploid giant cancer cells (PGCCs) have been observed by pathologists for over a century. PGCCs contribute to solid tumor heterogeneity, but their functions are largely undefined. Little attention has been given to these cells, largely because PGCCs have been generally thought to originate from repeated failure of mitosis/cytokinesis and have no capacity for long-term survival or proliferation. Here we report our successful purification and culture of PGCCs from human ovarian cancer cell lines and primary ovarian cancer. These cells are highly resistant to oxygen deprivation and could form through endoreduplication or cell fusion, generating regular-sized cancer cells quickly through budding or bursting similar to simple organisms like fungi. They express normal and cancer stem cell markers, they divide asymmetrically and they cycle slowly. They can differentiate into adipose, cartilage and bone. A single PGCC formed cancer spheroids in vitro and generated tumors in immunodeficient mice. These PGCC-derived tumors gained a mesenchymal phenotype with increased expression of cancer stem cell markers CD44 and CD133 and become more resistant to treatment with cisplatin. Taken together, our results reveal that PGCCs represent a resistant form of human cancer using an ancient, evolutionarily conserved mechanism in response to hypoxia stress; they can contribute to the generation of cancer stem-like cells, and also play a fundamental role in regulating tumor heterogeneity, tumor growth and chemoresistance in human cancer.

The concepts of 'sameness' and 'difference' in an insect

Insects process and learn information flexibly to adapt to their environment. The honeybee Apis mellifera constitutes a traditional model for studying learning and memory at behavioural, cellular and molecular levels. Earlier studies focused on elementary associative and non-associative forms of learning determined by either olfactory conditioning of the proboscis extension reflex or the learning of visual stimuli in an operant context. However, research has indicated that bees are capable of cognitive performances that were thought to occur only in some vertebrate species. For example, honeybees can interpolate visual information, exhibit associative recall, categorize visual information and learn contextual information. Here we show that honeybees can form 'sameness' and 'difference' concepts. They learn to solve 'delayed matching-to-sample' tasks, in which they are required to respond to a matching stimulus, and 'delayed non-matching-to-sample' tasks, in which they are required to respond to a different stimulus; they can also transfer the learned rules to new stimuli of the same or a different sensory modality. Thus, not only can bees learn specific objects and their physical parameters, but they can also master abstract inter-relationships, such as sameness and difference.

Animal models of Salmonella infections: enteritis versus typhoid fever

The most common disease syndromes caused by Salmonella serotypes in humans, typhoid fever and enteritis, can be modeled using Salmonella enterica serotype Typhimurium infections in mice and calves, respectively. This article reviews murine typhoid and bovine enteritis and discusses strengths, limitations and distinctive features of these animal models.

A Benzene-Thermal Synthetic Route to Nanocrystalline GaN

A thermal reaction of Li3N and GaCl3 in which benzene was used as the solvent under pressure has been carried out for the preparation of 30-nanometer particles of gallium nitride (GaN) at 280&deg;C. This temperature is much lower than that of traditional methods, and the yield of GaN reached 80%. The x-ray powder diffraction pattern indicated that sample was mainly hexagonal-phase GaN with a small fraction of rocksalt-phase GaN, which has a lattice constant a = 4.100 angstroms. This rocksalt structure, which had been observed previously only under high pressure (at least 37 gigapascals) was observed directly with high-resolution electron microscopy.

Activation of a mitogen-activated protein kinase pathway is involved in disease resistance in tobacco

Hypersensitive response (HR), a form of programmed cell death, is frequently associated with plant disease resistance. It has been proposed that mitogen-activated protein kinase (MAPK) cascades regulate HR cell death based on pharmacological studies by using kinase inhibitors. However, direct evidence is lacking. Here, we demonstrate that NtMEK2, a MAPK kinase, is upstream of salicylic acid-induced protein kinase (SIPK) and wounding-induced protein kinase (WIPK), two tobacco MAPKs that are activated by various pathogens or pathogen-derived elicitors. Expression of a constitutively active mutant of NtMEK2 induces HR-like cell death in tobacco, which is preceded by the activation of endogenous SIPK and WIPK. In addition, NtMEK2-SIPK/WIPK cascade appears to control the expression of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and l-phenylalanine ammonia lyase (PAL), two defense genes encoding key enzymes in the phytoalexin and salicylic acid biosynthesis pathways. These results demonstrate that a plant MAPK cascade controls multiple defense responses against pathogen invasion.

Salicylic acid activates a 48-kD MAP kinase in tobacco

The involvement of phosphorylation/dephosphorylation in the salicylic acid (SA) signal transduction pathway leading to pathogenesis-related gene induction has previously been demonstrated using kinase and phosphatase inhibitors. Here, we show that in tobacco suspension cells, SA induced a rapid and transient activation of a 48-kD kinase that uses myelin basic protein as a substrate. This kinase is called the p48 SIP kinase (for SA-Induced Protein kinase). Biologically active analogs of SA, which induce pathogenesis-related genes and enhanced resistance, also activated this kinase, whereas inactive analogs did not. Phosphorylation of a tyrosine residue(s) in the SIP kinase was associated with its activation. The SIP kinase was purified to homogeneity from SA-treated tobacco suspension culture cells. The purified SIP kinase is strongly phosphorylated on a tyrosine residue(s), and treatment with either protein tyrosine or serine/threonine phosphatases abolished its activity. Using primers corresponding to the sequences of internal tryptic peptides, we cloned the SIP kinase gene. Analysis of the SIP kinase sequence indicates that it belongs to the MAP kinase family and that it is distinct from the other plant MAP kinases previously implicated in stress responses, suggesting that different members of the MAP kinase family are activated by different stresses.