Isoforms pI Research Articles

Tektin B1 demonstrates flagellar localization in human sperm.

The human flagellar protein tektin B1 (h-tekB1) in human sperm was cloned, and its sequence and subcellular location were determined. Human sperm proteins were separated by 2-dimensional electrophoresis, and a resolved protein spot of 54 kDa with an isoelectric point (pI) of 5.3 was removed from the gel, trypsinized, and microsequenced by tandem mass spectrometry. The resulting peptides did not match any protein in the (then current) protein databases. Degenerate oligonucleotides based on the microsequences were used with a polymerase chain reaction to amplify a partial cDNA clone from human testis poly(A)(+) mRNA, and subsequently a full-length 1.5-kilobase (kb) clone (GenBank AF054910) was obtained from a testis cDNA library. The open reading frame encoded a 430-amino acid protein with 47% homology to the sea urchin tektin B1. Hybridization of labeled h-tekB1 cDNA to a multiple-tissue Northern blot demonstrated a transcript of 1.7 kb in human testis, and a multiple tissue dot-blot demonstrated high levels of expression in testis, trachea, and lung, intermediate levels in fetal brain and appendix, and low levels in ovary, pituitary, and fetal kidney. Rat polyclonal serum generated against a recombinant h-tekB1 demonstrated 3 h-tekB1 isoforms of pI 5.25, 5.5, and 5.35 at 53.5 kDa on a 2-dimensional Western blot of human sperm proteins. Immunofluorescent studies localized h-tekB1 to the principal piece of human sperm, but the endpiece was unstained.

A new generation of isoform-selective PI 3-K inhibitors

At least one ‘Holy Grail’ for many pharmaceutical research divisions has been to identify therapeutically useful selective PI 3-K inhibitors. There are several different, but closely related, PI 3-Ks, which are thought to have distinct biological roles. However, until now, medicinal chemists and biomedical researchers alike have been frustrated by the available pharmacological inhibitors, which are unable to distinguish the different isoforms of PI 3-K adequately. Fortunately, there seems to be light at the end of the tunnel; researchers at Thrombogenix Pty Ltd, Victoria, Australia have now reported the discovery of compounds with anti-thrombrotic properties that inhibit PI 3-Kα and PI 3-Kβ selectively, and might be of potential use for the treatment of patients with cardiovascular diseases. The idea of isoform-specific PI 3-K inhibitors now seems to be reality and might lead to the novel therapy of other PI-3-K-dependent conditions, such as respiratory diseases, inflammatory disorders, cancers and diseases linked to the disordered function of white blood cells. World Intellectual Property Organisation (2001) International Publication Number WO01/53266 A1 SW

Sensitization to the cytotoxicity of melphalan by ethacrynic acid and hyperthermia in drug-sensitive and multidrug-resistant Chinese hamster ovary cells.

The ability of physical and pharmacological modulators to increase the cytotoxicity of melphalan was investigated in Chinese hamster ovary cells using a clonogenic cell survival assay. Hyperthermia has potential for use in cancer treatment, particularly as an adjuvant to chemotherapy or radiotherapy. Ethacrynic acid is a glutathione S-transferase inhibitor and also undergoes conjugation with glutathione. Interactions between hyperthermia (41-43 degrees C), ethacrynic acid and melphalan were evaluated in multidrug-resistant (CH(R)C5) cells with overexpression of P-glycoprotein (33.69-fold), and in drug-sensitive (AuxB1) cells. GST alpha was expressed at a higher level (3.65-fold) in CH(R)C5 cells than in sensitive cells, whereas levels of isoforms pi and mu were the same. GST pi was the most highly expressed isoform in the two cell populations. Ethacrynic acid was cytotoxic at elevated temperatures, while it caused little or no cytotoxicity at 37 degrees C. This effect occurred in drug-resistant and drug-sensitive cells, and attributes thermosensitizing properties to ethacrynic acid. Ethacrynic acid (20 microM) alone did not alter the cytotoxicity of melphalan at 37 degrees C. Hyperthermia potentiated drug cytotoxicity in cells, both with and without ethacrynic acid treatment. Ethacrynic acid could be useful in cancer treatment by acting as a thermosensitizer when combined with heat and by enhancing the cytotoxicity of melphalan at elevated temperatures. A major advantage arising from the use of regional hyperthermia is the ability to target drug cytotoxicity to the tumor volume. A useful finding is that ethacrynic acid, heat and/or melphalan are also effective against multidrug-resistant cells with overexpression of P-glycoprotein.

Effect of NAA on the development, apoplastic peroxidase activities, and peroxidase isoenzymes in chicory root explants

Summary NAA significantly modified the growth of chicory (Cichorium intybus L. cv. Bea) root explants cultured for 12 d in either light or darkness. It also reduced the chlorophyll and the lignin content, peroxidase (EC 1.11.1.7) activities such as guaiacol peroxidase, auxin oxidase, and syringaldazine peroxidase in light as well as in darkness. There was a positive relationship between specific syringaldazine peroxidase activity and the lignin content, as well as between anionic peroxidases and lignification. Conversely, specific IAA oxidase activity and fresh weight were negatively correlated. NAA enhanced the expression of cationic peroxidase isoenzymes, particularly a peroxidase isoform pI 8.9 (Cicpx), in darkness and in light. This Cicpx was not involved in the lignification process. NAA is suggested as exerting an inhibitory effect on the biosynthetic pathways of tetrapyrrole-containing compounds.

Cloning and characterization of an 18 kiloDalton protein in the roots of the perennial weed Taraxacum officinale Weber (Dandelion) which has allergen- and pathogenesis-related protein properties

The root of the persistent weed, dandelion (Taraxacum officinale Weber), contains a predominant 18 kDa protein which undergoes small seasonal fluctuations in amount, increasing in the late autumn months, and declining in the spring. This protein has been purified and found to consist of two major isoforms of pI 5·56 and pI 5·49. A full-length cDNA has been obtained, coding for the pI 5·56 isoform, and the 156-amino-acid sequence deduced. The protein shows homologies in amino acid composition to several allergen and intracellular pathogenesis-related proteins. The deduced protein does not contain a signal peptide nor any known organelle-targeting sequences, and thus is likely to be cytosolic. Expression of the 18 kDa protein gene is exclusive to the roots and stem tissues; transcripts accumulate during the late autumn months, and decline in the early spring. Changes in the amount of protein in the root are much less. The mRNA for the 18 kDa protein is not present in the dry seed, but appears in the roots within 16–18 h from the start of imbibition, and is expressed constitutively thereafter. Although it is the predominant protein in dandelion roots, its properties are different from those commonly associated with vegetative storage proteins.

The influence of environmental pollution on the SOD and GST-isoenzyme patterns

The present study investigates the change of the specific isoenzyme pattern of superoxide dismutase (SOD) and glutathione S-transferases (GSTs) in the livers of sheep and fish after their exposure to metal pollutants (predominantly Cu, Hg, and Fe) in industrial areas. Moreover, the influence of mercury on the activities of antioxidant enzymes of rumen bacteria Streptococcus bovis and Selenomonas ruminantium have been studied. In the liver of sheep, the new SOD isoforms (pI 5.7, 5.3 and 5.1) were seen in polluted animals as well as in the liver of fish (pI 5.2, 5.1 and 4.45). With regard to GST isoenzymes, in the liver of sheep, subunit 1 was induced in polluted sheep, and subunit 3 was induced in both polluted sheep and fish liver. Subunit 7 was inactivated in sheep and fish liver. The SOD activity of S. bovis which was considered as Mn-SOD, increased when incubated with HgCl2 in both anaerobic and aerobic conditions. S. ruminantium showed no SOD activity. The differences in antioxidant activity between polluted and reference animals led us to propose that the induction of some isoenzymes of SOD and GSTs could provide useful biomarkers for monitoring environmental pollution.

Urinary Excretion of Glutathione S Transferases Alpha and Pi in Patients with Proteinuria: Reflection of the Site of Tubular Injury

In patients with renal diseases, proteinuria is a major determinant of progressive renal failure, probably by causing tubular cell injury. Little is known on extent and site of tubular cell injury in patients with proteinuria. Glutathione S transferases (GST) are cytosolic enzymes. The alpha isoform is present only in proximal tubular cells, whereas the pi isoform is confined to distal tubular cells. We have studied the urinary excretion of both isoenzymes in 56 (38 male and 18 female) patients with glomerular diseases and proteinuria. The mean age was 45 ± (SD) 16 years, the median creatinine clearance was 80 (range 27–159) ml/min, and the median albuminuria was 4.2 (range 0.7–16.9) g/10 mmol creatinine. The excretions of both GST alpha (median 35.9 ng/10 mmol creatinine) and GST pi (median 24.8 ng/10 mmol creatinine) were elevated as compared with control values (upper limits 10 and 12 ng/10 mmol creatinine, respectively). The urinary excretion of GST pi, but not that of GST alpha, was inversely correlated with the creatinine clearance. The highest levels of GST alpha were found in patients with a well-preserved renal function, whereas highest levels of GST pi were found in patients with renal failure. In a small number of patients we performed immunofluorescent studies of renal tissue. An increased urinary excretion of GST alpha correlated with brush border damage and decreased staining of proximal tubules for that isoenzyme. Our data suggest that in patients with proteinuria initial injury is apparent at the proximal tubules. Measurements of GST alpha and GST pi appear useful to study longitudinal timing and site of proteinuria-induced tubular cell injury.

Cadmium-mediated oxidative stress in alveolar epithelial cells induces the expression of gamma-glutamylcysteine synthetase catalytic subunit and glutathione S-transferase alpha and pi isoforms: potential role of activator protein-1.

Exposure of rat alveolar epithelial cells to 10 micromol/L CdCl2 causes time-dependent increases in steady-state mRNA levels of the gamma-glutamylcysteine synthetase catalytic (heavy) subunit (gamma-GCS) and of glutathione S-transferase isoforms (GST-alpha and GST-pi). The expression of gamma-GCS was significantly increased as early as 2 h after addition of cadmium. Maximal induction of gamma-GCS mRNA (approximately 4-fold), at 8 h, was subsequently followed by increases in gamma-GCS activity/protein and glutathione (GSH) levels. Maximal elevations in GST-pi (approximately 2-fold) and GST-alpha (approximately 10-fold) transcripts, at 8 and 24 h, respectively, were also accompanied by enhanced GST activity. Cadmium-induced oxidative stress, assessed by alterations in GSH homeostasis and an accelerated rate of intracellular oxidant production, could constitute early events in the signal transduction pathway mediating these responses. The dimeric transcription factor, activator protein-1 (AP-1), may also play a regulatory role in this process. This association is suggested by transcriptional activation of the immediate-early response genes, c-fos and c-jun, within 15 min after exposure to cadmium and by the enhancement of AP-1 DNA binding activity, involving a c-Jun protein complex, which is maximally induced (approximately 4-fold) by 2 h. These molecular changes likely function together to protect alveolar epithelial cells against cadmium toxicity.

Induction of β -1,3-glucanase in Seedlings of Pearl Millet in Response to Infection by Sclerospora graminicola

Differential resistance of pearl millet cultivars to downy mildew disease was correlated with the levels of β-1,3-glucanase in their seeds. Higher activity of the enzyme in highly resistant cultivars and lower activity in the highly susceptible ones suggested the possible use of β-1,3-glucanase as a biochemical marker for screening pearl millet cultivars for downy mildew disease. Inoculation of seedlings with the downy mildew pathogen Sclerospora graminicola resulted in increased enzyme levels in resistant cultivars. Mesocotyl and shoot regions of seedlings recorded higher levels of enzyme than the root. Isoelectric focusing revealed four basic isoforms with pI 9.6, 9.0, 8.9 and 8.2 and two acidic isoforms with pI 4.9 and 6.2 of β-1,3-glucanase in pearl millet. The pI 9.6 isoform was a major isoform of the enzyme in the pearl millet seedlings with a probable developmental function. Isoforms pI 6.2 and pI 8.2 appeared to be involved in resistance and pI 4.9 isoform seemed to be involved in pathogenesis of pearl millet-downy mildew.

Crystallization and preliminary crystal analysis of yeast hexokinase PI and PII.

Hexokinase is the prime enzyme of the Embden-Meyerhof pathway and is responsible for the first stage of energy conversion. It catalyzes the transfer of a phosphate to glucose to form glucose-6-phosphate. Yeast hexokinase PII is also known to play an important role in glucose signal transduction. Crystals of yeast hexokinase isoforms PI and PII were obtained by vapour-diffusion techniques using the hanging-drop method. Isoform PI crystals belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 62.12, b = 78.87, c = 144.74 A. Unit-cell parameters for isoform PII crystals are a = b = 142.81, c = 58.46 A and the space group is I4. Synchrotron diffraction data have been collected to 2.2 A resolution from the isoform PII crystal, whereas isoform PI diffracted to 3.1 A.

Molecular mechanism for sodium-dependent activation of G protein-gated K+ channels.

1. G protein-gated inwardly rectifying K+ (GIRK) channels are activated independently by Gbetagamma and internal Na+ via mechanisms requiring phosphatidylinositol phosphates. An aspartate (Asp) at position 226 in GIRK2 is crucial for Na+-dependent activation of GIRK1-GIRK2 heteromeric channels. We expressed wild-type and mutant GIRK1-GIRK2 channels in Xenopus oocytes and tested the effects of Na+ and neutralizing Asp226 on the functional interactions of the channels with phosphatidylinositol 4, 5-bisphosphate (PIP2). 2. The rate of inhibition of GIRK1-GIRK2 currents by application of anti-PIP2 antibody to inside-out membrane patches was slowed > 2-fold by the D226N mutation in GIRK2 and by increasing internal [Na+]. The reverse mutation in GIRK1 (N217D) increased the rate of inhibition. 3. The dose-response relationship for activation by purified PIP2 was shifted to lower concentrations in the presence of 20 mM Na+. 4. Three synthetic isoforms of PIP2, PI(4,5)P2, PI(3,4)P2 and PI(3,5)P2, activated GIRK channels with similar potencies. 5. We conclude that Na+ directly interacts with Asp226 of GIRK2 to reduce the negative electrostatic potential and promote the functional interaction of the channels with PIP2.

Actin Residue Glu93 Is Identified as an Amino Acid Affecting Myosin Binding

Many mutants have been described that affect the function of the actin encoded by the Drosophila melanogaster indirect flight muscle-specific actin gene, Act88F. We describe the development of procedures for purification of this actin from the other isoforms expressed in the fly as well as in vitro motility, single molecule force/displacement measurements, and stop-flow solution kinetic studies of the wild-type actin and that of the E93K mutation of the Act88F gene. We show that this mutation affects in vitro motility of F-actin, in both the presence and absence of methylcellulose, and the ability of the ACT88F actin to bind the S1 fragment of rabbit skeletal myosin. However, optical tweezer measurements of the actomyosin working stroke and the force transmitted from the rabbit heavy meromyosin to and through F-actin are unchanged by the mutation. These results support the proposal (Holmes, K. C. (1995) Biophys J. 68, (suppl.) 2-7) that actin residue Glu(93) is part of the secondary myosin binding site and suggest that myosin binding occurs first at the primary myosin binding site and then at the secondary site.

Indole-3-Acetic Acid Control on Acidic Oat Cell Wall Peroxidases.

Incubation of oat coleoptile segments with 40 µm indoleacetic acid (IAA) induced a decrease of 35-60% in peroxidase activity at the cell wall compartment. Treatment with IAA also produced a similar decrease in the oxidation of NADH and IAA at the cell wall. Isoelectric focusing of ionic, covalent, and intercellular wall peroxidase fractions showed that acidic isoforms (pI 4.0-5.5) were reduced preferentially by IAA treatment. Marked differences were found between acidic and basic wall isoperoxidases in relation to their efficacy in the oxidation of IAA. A peroxidase fraction containing acidic isoforms oxidized IAA with a V(max)/s(0.5) value of 2.4 x 10(-2) min(-1). g fw(-1), 4.0 times higher than that obtained for basic peroxidase isoforms (0.6 x 10(-2) min(-1). g fw(-1)). In contrast, basic isoforms were more efficient than acidic isoperoxidases in the oxidation of coniferyl alcohol or ferulic acid with H(2)O(2) (5.6 and 2.1 times, respectively). The levels of diferulate and lignin in the walls of oat coleoptile segments were not altered by treatment with IAA. The decrease in cell wall peroxidase activity by IAA was related more to reduced oxidative degradation of the hormone than to covalent cell wall cross-linking.Key Words. IAA-Auxin-Wall peroxidases-Oat-Avena sativa-Diferulic acid-Ligninhttp://link.springer-ny.com/link/service/journals/00344/bibs/18n1p25.html

Influence of light conditions on development, apoplastic peroxidase activities and peroxidase isoenzymes in chicory root explants

Cichorium intybus L. (cv. Bea) root explants grown in continuous light had a higher fresh weight, lignin and chlorophyll content than explants grown in darkness. Intermediary values were found when the light conditions were switched after 6 days. Peroxidase activities (EC 1.11.1.7) were measured in the apoplastic fluid with guaiacol, indoleacetic acid (IAA) and syringaldazine as substrates. There was an inverse relationship between specific IAA oxidase activity and explant growth. Specific syringaldazine oxidase activity (SSO) correlated with the lignin content. Analysis by isoelectric focusing (IEF) showed that the apoplastic fluid contained both cationic and anionic peroxidase isoforms, whose expression differed according to culture conditions. Isoform isoelectric point (pI) 7.0 was only detectable when the explants were cultured for 12 days in darkness. When explants were grown for the first 6 days in light, SSO and lignin content were high and the isoforms pI 4.0, 6.6, 7.6 and 8.1 were highly expressed. Conversely, when the first 6 days were in darkness, specific IAA oxidase activity was high and the isoforms pI 4.5, 6.7 and 6.8. were most strongly expressed. The isoperoxidases pI 7.8 and 7.9 were strongly expressed when the explants were cultured for at least 6 days in darkness.

Characterization of human insulin-like growth factor-binding proteins by two-dimensional polyacrylamide gel electrophoresis and Western ligand blot analysis.

The insulin-like growth factor (IGF)-binding proteins (IGFBPs) from adult human serum, amniotic fluid, and cerebrospinal fluid were analyzed by a modified two-dimensional gel electrophoresis followed by Western ligand blotting. The samples were subjected to immobilized pH gradient isoelectric focusing in the first dimension, followed by nondenaturing SDS-PAGE in the second dimension and autoradiography after ligand blotting with [125I]IGF-I or [125I]IGF-II. The identity of the binding proteins was confirmed by immunoblotting and immunoprecipitation with specific antibodies. Using this method, all six human high affinity IGFBPs could be clearly separated from each other according to their molecular mass and isoelectric points (pI). All IGFBPs exhibited a variety of specific pI isoforms, which presumably represent posttranslational modifications. In adult human serum, glycosylated IGFBP-3 is found as a broad band of spots with molecular masses of 41 and 45 kDa and a pI in the range of 4.8-8.2. The two IGFBP-3 bands could be reduced to a single 36-kDa band after deglycosylation (pI 6-9). Furthermore, the specific spots for IGFBP-2 (33 kDa; pI 6.2-7.1) and deglycosylated IGFBP-4 (24 kDa; pI 6.3, 6.5, and 6.8) were found with their expected molecular masses. Additionally, the diffuse bands around 30 kDa, found in one-dimensional Western ligand blotting, could be clearly separated into distinct groups of specific spots representing IGFBP-1 (30 kDa; pI 4.0-4.8), IGFBP-6 (30 kDa; pI 4.8-5.8), glycosylated IGFBP-4 (29 kDa; pI 6.1 and 6.3), and IGFBP-5 (30/31 kDa; pI 6.4-8). As expected, IGFBP-6 was visible only when IGF-II was used as radioligand. In conclusion, two-dimensional gel electrophoresis followed by Western ligand blotting allows identification of all six high affinity IGFBPs with their isoforms on the basis of their characteristic molecular masses and pI, especially in the range of 30 kDa. This technique can be rapidly performed with small amounts of complex biological fluids and is a powerful tool for the detection and analysis of posttranslational modifications of IGFBPs.

Differential Expression of Glutathione S-Transferases in Germ Cell Tumors of Human Testes

Glutathione S-transferase (GST) isoenzymes alfa, mu and pi were assessed by Western blotting in normal testes, seminomas and non-seminomatous germ cell tumors (NSGCTs). GST alfa and mu were strongly expressed in all normal specimens (n = 6), the pi isoform, however, could not or barely be detected. Ten (92%) of 11 seminomas had GST pi and only 2 (16%) showed alfa expression. In contrast, twelve (80%) of 15 NSGCTs showed a significant level of GST alfa and only 2 (13%) had GST pi expression. The absence or paucity of mu isoform was characteristic for all neoplastic testicular tissues. A statistically significant relationship (P = 0.021) could be established between GST alfa and stages of disease, i.e., alfa isoform was prevalent in the later stage (IIB, III) NSGCT tumors. These results suggest that the poor prognosis of the later stage NSGCTs may be due to their high GST alfa content, while the GST pi does not seem to have role in this relation.

Actin expression in germinating seeds of Phaseolus vulgaris L.

Actin was present at very low levels in the seeds of common bean (Phaseolus vulgaris L.) compared with those from other species, and was observed mostly in the embryo. A time-course of actin expression in germinating bean seeds revealed an induced expression of both the mRNA and protein. Initially, the actin mRNA in seeds was barely detectable by northern blot analysis. However, there was a substantial increase in the expression of the actin mRNA at 24, 48 and 72 h after imbibition, compared with an internal control consisting of a late-embryogenesis-abundant (LEA) type IV gene from P. vulgaris. An increase in the amount of actin in total seed extracts that parallelled that of the mRNA was detected by western blotting starting at 24 h after imbibition. This increase was more apparent when the embryo alone was analyzed. Two-dimensional west-ern blots initially revealed three actin isoforms with isoelectric points (pIs) of approximately 5.6, 5.7 and 5.8,the amounts of which increased within a 48-h period,when a new minor isoform of pI approximately 5.5 appeared; however, after 72 h, the pI-5.8 isoform had almost disappeared and the pI-5.5 isoform had disappeared completely, indicating that these two minor isoforms are expressed transiently. These results indicate that actin is at very low levels in the dry seed but undergoes an increased and differential expression during imbibition, an event probably required to carry out all the necessary functions for germination.

Characterization of tyrosinase from the cap flesh of portabella mushrooms.

Tyrosinase, purified from the cap flesh tissue of portabella mushrooms, was characterized with regard to its physical and biochemical properties. A native molecular size of 41 kDa for the enzyme was obtained by size exclusion chromatography, whereas SDS-PAGE indicated that the enzyme contained a single subunit with a size of approximately 48 kDa under reduced and nonreduced conditions. The purified enzyme showed a single immunological cross-reacting protein after Western blotting when probed with antibodies against Agaricus bisporus tyrosinase. Isoelectric focusing demonstrated that the enzyme preparation, apparently homogeneous by electrophoresis, still contained three isoforms of pI 5.1, 5.2, and 5.3. The purified enzyme was able to oxidize a variety of mono-, di-, and triphenolic compounds. An apparent K(m) of 5 mM was obtained using catechol as the substrate, and an apparent K(m) of 9 mM was found using L-Dopa as a substrate. Ascorbic acid, kojic acid, tropolone, mercaptobenzothiazole, and salicylhydroxamic acid inhibited the enzyme severely at 100 microM.

A Requirement for Phosphatidylinositol 3-Kinase in Pseudopod Extension

Phagocytosis requires actin assembly and pseudopod extension, two cellular events that coincide spatially and temporally. The signal transduction events underlying both processes may be distinct. We tested whether phagocytic signaling resembles that of growth factor receptors, which induce actin polymerization via activation of phosphatidylinositol 3-kinase (PI 3-kinase). Fcgamma receptor-mediated phagocytosis was accompanied by a rapid increase in the accumulation of phosphatidylinositol 3,4,5-trisphosphate in vivo, and addition of wortmannin (WM) or LY294002, two inhibitors of PI 3-kinase(s), inhibited phagocytosis but not Fcgamma receptor-directed actin polymerization. However, both compounds prevented maximal pseudopod extension, suggesting that PI 3-kinase inhibition produced a limitation in membrane required for pseudopod extension. Availability of plasma membrane was not limiting for phagocytosis, because blockade of ingestion in the presence of WM was not overcome by reducing the number of particles adhering to macrophages. However, decreasing bead size, and hence the magnitude of pseudopod extension required for particle engulfment, relieved the inhibition of phagocytosis in the presence of WM or LY294002 by up to 80%. The block in phagocytosis of large particles occurred before phagosomal closure, because both compounds inhibited spreading of macrophages on substrate-bound IgG. Macrophage spreading on IgG was accompanied by exocytic insertion of membrane from an intracellular source, as measured by the dye FM1-43. These results indicate that one or more isoforms of PI 3 kinase are required for maximal pseudopod extension but not phagocytosis per se. We suggest that PI 3-kinase is required for coordinating exocytic membrane insertion and pseudopod extension.

Small genes/gene-products in Escherichia coli K-12.

Forty-two protein spots of observed M(r) 6-15 kDa were resolved by two-dimensional gel electrophoresis, stained by Coomassie blue and subjected to Edman microsequencing. All of the proteins could be related back to their encoding open reading frames, thereby vindicating the bioinformatic tools currently utilised in their identification. However, only 14/42 gene-products were expressed as annotated. Translation was confirmed for 14 open reading frames with no attributed function (EcoGene Y-entries), while N-terminal sequence allowed the start codon to be accurately annotated for the genes yigF, yccU, yqiC, ynfD, and yeeX. The methionine start codon was cleaved in 11 gene-products (AtpE, Hns, RpoZ, RplL, CspC, YccJ, YggX, YjgF, HimA, InfA, RpsQ) and a further five showed loss of a signal peptide (PspE, HdeB, HdeA, YnfD, YkfE). Internal (Tig, AtpA, TufA) and N-terminal fragmentation (CspD, RpsF, AtcU) of much larger proteins was also detected, which may have resulted from physiological or translational processes. M(r) and pI isoforms were detected respectively for PtsH and GatB, each being phosphoproteins, as well as RplY which manifested differences with respect to predicted M(r) and pI. In addition, YjgF was shown to belong to a small gene family of unknown function with ancient conserved regions across procaryotes and eucaryotes. YgiN was revealed to have a paralogue and orthologues in Bacillus subtilis, Synechocystis sp., Mycobacterium tuberculosis, Neisseria gonorrhoea, and Rhodococcus erythropolis. Orthologues are also reported for YihD, YccU and YeeX. Of the 14 Y-genes, only YkfE possessed no detectable orthologues. These results highlight the need to complement genomic analysis with detailed proteomics in order to gain a better understanding of cellular molecular biology, while the confirmation of the open reading frame start codon using Edman degradation protein microsequencing has yet to be superseded by recent advances in mass spectrometry.