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Biomedical subjects

P C John

Publications and source records attributed to P C John.

At least 19 recordsLinked to original sources
PubMed2001

Cyclin/Cdk complexes: their involvement in cell cycle progression and mitotic division.

DNA replication and mitosis are dependent on the activity of cyclin-dependent protein kinase (CDK) enzymes, which are heterodimers of a catalytic subunit with a cyclin subunit. Cyclin binding to specific individual proteins is thought to provide potential substrates to Cdk. Protein binding by cyclins is assessed in terms of its mechanisms and biological significance, using evidence from diverse organisms including substrate specificity in animal Cdk enzymes containing D-, A-, and B-type cyclins and extensive cyclin gene manipulations in yeasts. Assembly of protein complexes with cyclin/Cdk is noted and the capacity of the cyclin-dependent kinase subunit Cks, in such complex, to extend the range of Cdk substrates is documented and discussed in terms of cell cycle regulation. Cell cycle progression involves changing abundance of individual cyclins, due to changing rates of their transcription or proteolysis, with consequent changes in the substrates of CDK through the cell cycle. Some overlap of the functions of individual cyclins in vivo has been identified by cyclin deletions and is suggested to follow a pattern in which cyclins can commonly complete functions initiated by the preceding cyclins well enough to preserve viability as groups of cyclins are removed by proteolysis. Cyclin accumulation is particularly important in terminating the G1 phase, when it raises CDK activity and starts events leading to DNA replication. It is suggested that plants share this mechanism. The distribution of cyclins and Cdk in maize root tip cells during mitosis and cytokinesis indicates the presence of Cdk1 (Cdc2a) and cyclin CycB1zm;2 at the mature and disassembling preprophase band and the presence of CycB1zm;2 at condensing and condensed chromosomes. Both observations correlate with the earlier-reported capacity of injected metaphase cyclin/CDK to accelerate preprophase band disassembly and chromosome condensation and with observations of the location of Cdk and cyclins in other laboratories. Additionally CycB1zm;2 is seen at the nuclear envelope during its breakdown, which correlates with an acceleration of the process by injected metaphase cyclin B/CDK. A phenomenon possibly unique to the plant kingdom is the persistence of mitotic cyclins after anaphase. Participation of cyclins in cytokinesis is indicated by the concentration of the mitotic cyclin CycA1;zm;1 at the phragmoplast. It is suggested that cyclins have a general function of spatially focusing Cdk activity and that in the plant cell the concentrations of cyclins are important mediators of CDK activity at the cytoskeleton, chromosomes, spindle, nuclear envelope, and phragmoplast.

Animals↗
PubMed1998

Merit of mobilization technique in transfer of non-autotransferable R-plasmids.

A total of 200 urinary isolates of Esch.coli received at National Salmonella and Escherichia Centre, Central Research Institute, Kasauli during the years 1995 to 1997 were studied for transferable drug resistance. Out of 188 strains, 134 strains showing resistance to either Nalidixic acid or Rifampicin were subjected to autotransferable resistance studies. Of these 134 strains 131 showed either partial or enbloc transfer of R-factor. Mobilization experiment successfully transferred resistance marker in 14 of the 68 isolates in which resistance to one or more drugs could not be transferred during conjugation experiment.

Drug Resistance, Microbial↗
PubMed1998

Prevalance and resistance pattern of Salmonella serotypes in India.

During the period 1990-91, 3222 Salmonella strains were identified at the National Salmonella and Escherichia Centre (NSEC) at Central Research Institute, Kasauli. Of these, 2894 were from humans, 226 from poultry, 84 from animals and remaining 18 from reptiles, birds and other sources. These strains belonged to 53 different serotypes. These include 4 serotypes reported for the first time in India, namely S. kedogou, S. VP. bornheim, S. kisarawe and S. madras. Drug resistance studies revealed that 573 strains were sensitive to all the antibiotics commonly used, 1351 single drug resistant, 594 resistant to two drugs and 704 were multidrug resistant. One strain from human stool was resistant to all the antibiotics used. Prevalence of various Salmonella serotypes and their response to various drugs is discussed.

Animals↗
PubMed1996

Plant mitosis promoting factor disassembles the microtubule preprophase band and accelerates prophase progression in Tradescantia.

The regulation of mitosis in higher plant cells has been investigated by microinjecting protein kinase from the metaphase-arresting (met1) mutant of Chlamydomonas. Biochemical characterization of this enzyme complex confirms the presence of a p34cdc2/cyclin B-like kinase. The enzyme was injected into living stamen hair cells of Tradescantia virginiana in which microtubules (MTs) were visualized using fluorescent analogue cytochemistry and confocal laser scanning microscopy. Microinjection of this p34cdc2/cyclin B-like kinase caused rapid disassembly of the preprophase band of MTs but not of interphase-cortical, spindle or phragmoplast MTs. Effects of the enzyme on the cytomorphology of live prophase cells were also monitored using video microscopy. We found that injection of this enzyme accelerated chromatin condensation and nuclear envelope breakdown. This indicates the presence and function in plants of an enzyme that can initiate nuclear division similar to the maturation or mitosis promoting factor (MPF) of animal cells. These studies provide the first direct evidence that the mitotically-active form of plant MPF can drive disassembly of preprophase band MTs, chromosome condensation and initiation of mitosis in plant cells.

Animals↗
PubMed1996

The plant cell cycle: conserved and unique features in mitotic control.

Somatic plant cells can use a hormone checkpoint in late G2 phase. Here cytokinin stimulates removal of phosphotyrosine from p34cdc2 kinase and concurrently capacity for activation of the kinase by Cdc25 phosphatase declines while activity of the kinase increases and cells enter mitosis. Processes unique to plant mitosis are driven by the mitotically active kinase since the enzyme taken from plant cells in metaphase, when injected, can disassemble the preprophase band microtubules that form in G2 phase at the site of the future cross wall. This action is specific, since microtubules are not depolymerised when in interphase cytoplasmic array, or spindle, or phragmoplast. Plant metaphase kinase acts as MPF by accelerating chromosome condensation and nuclear envelope breakdown.

Amino Acid Sequence↗
PubMed1996

Cytokinin controls the cell cycle at mitosis by stimulating the tyrosine dephosphorylation and activation of p34cdc2-like H1 histone kinase.

In excised pith parenchyma from Nicotiana tabacum L. cv. Wisconsin Havana 38, auxin (naphthalene-1-acetic acid) together with cytokinin (6-benzylaminopurine) induced a greater than 40-fold increase in a p34cdc2-like protein, recoverable in the p13suc1-binding fraction, that had high H1 histone kinase activity, but enzyme induced without cytokinin was inactive. In suspension-cultured N. plumbaginifolia Viv., cytokinin (kinetin) was stringently required only in late G2 phase of the cell division cycle (cdc) and cells lacking kinetin arrested in G2 phase with inactive p34cdc2-like H1 histone kinase. Control of the Cdc2 kinase by inhibitory tyrosine phosphorylation was indicated by high phosphotyrosine in the inactive enzyme of arrested pith and suspension cells. Yeast cdc25 phosphatase, which is specific for removal of phosphate from tyrosine at the active site of p34cdc2 enzyme, was expressed in bacteria and caused extensive in-vitro activation of p13suc1-purified enzyme from pith and suspension cells cultured without cytokinin. Cytokinin stimulated the removal of phosphate, activation of the enzyme and rapid synchronous entry into mitosis. Therefore, plants can control cell division by tyrosine phosphorylation of Cdc2 but differ from somatic animal cells in coupling this mitotic control to hormonal signals.

Amino Acid Sequence↗
PubMed1996

Adjuvant effect of DEAE-dextran and tetanus toxoid on whole cell heat inactivated phenol preserved typhoid vaccine.

Active mouse protection test (AMPT) and enzyme linked immunosorbent assay (ELISA) were used to determine the immunogenicity of whole cell typhoid vaccine when administered in conjunction with either tetanus toxoid (TT) or DEAE-Dextran (DD). Immunization of mice with whole cell typhoid vaccine showed enhanced potency either when administered in conjunction with TT or DD and values were statistically significant (p < 0.05) in comparison to conventional or standard typhoid vaccines. For ELISA, the mice were immunized with 2 different schedules, one in which a single dose of 0.25 ml subcutaneously (s/c) was administered and in another two doses of 0.25 ml each s/c, 14 days apart. In case of single dose schedule of immunization D vaccine (Whole cell typhoid + 5 mg/ml DD) showed significant increase of immune response (3.201 log10) as compared to plain vaccine (2.550 log10). Two dose schedule further increased the titres to 3.856 log10. DD adjuvanted vaccine showed higher potency by AMPT as compared to the TT adjuvanted vaccine or plain vaccine. The present study clearly demonstrates that a single dose of 0.25 ml which is equivalent to half of the conventionally used single human dose of typhoid vaccine adjuvanted with DD can significantly improve the immunogenicity of the vaccine.

Adjuvants, Immunologic↗
PubMed1994

Nuclear concentration and mitotic dispersion of the essential cell cycle protein, p13suc1, examined in living cells.

Stamen hair cells of Tradescantia virginiana have been microinjected with p13suc1 labeled with carboxyfluorescein (CF) and studied throughout the division cycle in living cells by using the confocal laser scanning microscope. The protein, p13suc1, is essential for the rapid inactivation of the key mitotic catalyst, p34cdc2 kinase, at anaphase and for completion of nuclear division. During interphase or prophase, CF-p13suc1 concentrates quickly (< 2 min) in nuclei, reaching levels that are approximately 2-fold greater than those in the cytoplasm. At nuclear envelope breakdown, CF-p13suc1 permeates throughout the entire spindle and nonspindle cytoplasm. The protein is excluded from the tightly condensed chromosomes but otherwise no regions accumulate or exclude the protein. It remains evenly distributed throughout metaphase, anaphase, and well into cytokinesis; however, during telophase CF-p13suc1 reconcentrates in the daughter nuclei.

Cell Cycle Proteins↗
PubMed1994

Bacteriophage typing in Salmonella bareilly.

A total of 675 strains of Salmonella bareilly received from different parts of India and France during 1959-92 were phage typed using six bacteriophages. Overall typability achieved was 90.8% with 23 distinct phage types excluding a group of untypable strains. Phage types have been defined in octal code. Simpson's coefficient was applied for diversity index having a value of 0.839. This system was found to be reproducible, stable and epidemiologically useful.

Animals↗
PubMed1994

Transferable beta lactam resistance against cephalosporins in Salmonella typhimurium strains in India.

From 14 strains of S. typhimurium which were resistant to three cephalosporins (cephalexin, cefadroxil and sodium cefotaxime) the resistance plasmids were transferred to two different strains (Escherichia coli K12F-Lac-Rifr and S. typhimurium LT2). The plasmids were autotransferable and the donors as well as transconjugants showed high levels of MIC (80-320 micrograms/ml or more) against these antimicrobial agents. The resistance was demonstrated to be mediated by a 15 kilobase plasmid.

Cefadroxil↗
PubMed1993

Prevalence of copper resistant salmonellae in India.

Sixty eight of 330 strains of Salmonella belonging to three different serotypes, S. typhi, S. typhimurium and S. bareilly, referred to at the National Salmonella and Escherichia Centre, Central Research Institute, Kasauli, between 1989-1991 were found to be copper resistant. Maximum number of strains (39.1%) were resistant in S. bareilly serotype, followed by S. typhimurium (21.7%) and least in S. typhi (17.4%). Of the 15 States/Union Territories (UTs) from where Salmonella strains were received, copper resistance was observed in strains from 10 States/UTs. This resistance was maximum among the strains from Goa (85.7%).

Copper↗
PubMed1992

Actin dynamics during the cell cycle in Chlamydomonas reinhardtii.

We have used two monoclonal antibodies to demonstrate the presence and localization of actin in interphase and mitotic vegetative cells of the green alga Chlamydomonas reinhardtii. Commercially available monoclonal antibodies raised against smooth muscle actin (Lessard: Cell Motil. Cytoskeleton 10:349-362, 1988; Lin: Proc. Natl. Acad. Sci. USA 78:2335-2339, 1981) identify Chlamydomonas actin as a approximately 43,000-M(r) protein by Western immunoblot procedures. In an earlier study, Detmers and coworkers (Cell Motil. 5:415-430, 1985) first identified Chlamydomonas actin using NBD-phallacidin and an antibody raised against Dictyostelium actin; they demonstrated that F-actin is localized in the fertilization tubule of mating gametes. Here, we show by immunofluorescence that vegetative Chlamydomonas cells have an array of actin that surrounds the nucleus in interphase cells and undergoes dramatic reorganization during mitosis and cytokinesis. This includes the following: reorganization of actin to the anterior of the cell during preprophase; the formation of a cruciate actin band in prophase; reorganization to a single anterior actin band in metaphase; rearrangement forming a focus of actin anterior to the metaphase plate; reextension of the actin band in anaphase; presence of actin in the forming cleavage furrow during telophase and cytokinesis; and finally reestablishment of the interphase actin array. The studies presented here do not allow us to discriminate between G and F-actin. None the less, our observations, demonstrating dynamic reorganization of actin during the cell cycle, suggest a role for actin that may include the movement of basal bodies toward the spindle poles in mitosis and the formation of the cleavage furrow during cytokinesis.

Actins↗
PubMed1991

Increasing prevalence of high degree resistance amongst Salmonella to different antibiotics.

National Salmonella & Escherichia Centre situated at Central Research Institute, Kasauli receives Salmonella strains from all over the country. Eight hundred and fourteen Salmonella strains belonging to 14 serotypes received during 1986 were studied for antibiotic resistance and Minimum Inhibitory concentration (MIC) with regard to ampicillin (A), chloramphenicol (C), furazolidone (Fz) and gentamicin (G). Resistance to ampicillin was found to be highest (80%) and furazolidone the least (0.1%). Similarly a large number of strains (31%) had very high MIC values greater than 640 mcg per ml for chloramphenicol, whereas only 3.4% strains were found to have MIC values greater than 640 mcg per ml for gentamicin. The present findings have been discussed in the light of similar data published from this Centre earlier and from other sources in India.

Ampicillin↗
PubMed1990

p34cdc2 homologue level, cell division, phytohormone responsiveness and cell differentiation in wheat leaves.

Formation of a plant involves generation of new cells by the division cycle and development in these of specialised structure and metabolism. Specialisation is accompanied by a decreasing capacity for division, which declines with particular rapidity in cells of monocotyledonous plants such as the cereals. Here we report that in wheat leaves a homologue of the cell cycle control protein p34(cdc2) participates in the control of these developmental programmes. Accumulation of p34(cdc2) to a maximum level in dividing cells and the cessation of its accumulation during subsequent cell growth and expansion indicate that it contributes specifically to division. There is a decline in p34(cdc2) level as cell differentiation proceeds, in close parallel with the previously established decline of cell division in response to auxin hormones. A basal level of p34(cdc2) in fully differentiated cells that is one-sixteenth of that in dividing cells correlates with their loss of capacity to divide. We conclude that p34(cdc2) level is controlled in diverse multicellular eukaryotes and suggest that it is an important element in the switch from cell division to differentiation.

Amino Acid Sequence↗
PubMed1990

The mitosis-specific monoclonal antibody MPM-2 recognizes phosphoproteins associated with the nuclear envelope in Chlamydomonas reinhardtii cells.

The monoclonal antibody MPM-2 recognizes a family of phosphorylated proteins present in mitotic cells. In a number of organisms it stains nuclei and also cytoskeletal structures which contain or organize tubulin. In mitotic Chlamydomonas reinhardtii cells MPM-2 reacts with phosphoproteins associated with the nuclear envelope (NE). Staining of the NE region appears in preprophase, reaches a maximum intensity in metaphase/anaphase and disappears rapidly in telophase. Localized hyperphosphorylation of the anterior NE region is apparent in many cells throughout mitosis. The distribution and timing of MPM-2 labeling suggests that in Chlamydomonas MPM-2 may be interacting with lamin-like phosphoproteins.

Antibodies, Monoclonal↗