Long-term use of IgA-depleted intravenous immunoglobulin in immunodeficient subjects with anti-IgA antibodies

The use of intravenous immunoglobulin is standard practice for antibody replacement in the humoral immunodeficiency diseases. Most infusions proceed uneventfully, but a proportion of infusions (5-8%) produces some degree of an infusion reaction. While the cause of most of these infusion reactions is unknown, an established, but rare cause of reactions is IgA antibodies in the serum of the patient, which apparently forms an immune complex with the traces of IgA in the infused immunoglobulin. This article describes our studies of five immunodeficient patients who had high-titered anti-IgA antibodies and a history of severe infusion reactions to intravenous immunoglobulin products not depleted of IgA (IgA content, 270-720 micrograms/ml). Over a 6-year period we gave these patients IgA-depleted intravenous immunoglobulin for a total of 170 infusions. These infusions were generally well tolerated; however, mild to moderate infusion reactions did occur in 9 of the 170 infusions (5.3%). These reactions were not related to the IgA content of the immunoglobulin solutions used--ascertained to vary between 0.4 and 2.9 micrograms/ml of IgA. Levels of plasma C3a and C4a increased after immunoglobulin infusions but the appearance of these components was not accompanied by any infusion reaction. We conclude that the long-term infusions of IgA-depleted intravenous immunoglobulin, within the range of IgA concentrations investigated, into patients with even very high-titered antibodies to IgA, is a safe practice.

Fractional contribution of calcium to the cation current through glutamate receptor channels

The Ca2+ fraction of the ion current flowing through glutamatergic NMDA and AMPA/kainate receptor channels was determined in forebrain neurons of the medial septum. The neurons were overloaded with the Ca2+ indicator dye fura-2 (1 mM) via the recording patch pipettes. This approach allowed the direct determination of the Ca2+ influx from changes in the Ca(2+)-sensitive fura-2 fluorescence. We found that, at negative membrane potentials and at an extracellular free Ca2+ concentration of 1.6 mM, the Ca2+ fraction of the current through the NMDA receptor channels is only 6.8%, about 2-fold lower than previously estimated from reversal potential measurements. Interestingly, a quite high fractional Ca2+ current of 1.4% was determined for the linearly conducting AMPA/kainate receptor channels found in these neurons.

Na(+)-Ca2+ exchange current in latent pacemaker cells isolated from cat right atrium

1. Single latent pacemaker cells were isolated from cat right atrium, and studied in a whole-cell configuration using a nystatin-perforated patch recording method. The nystatin method avoids alterations in intracellular Ca2+, cellular constituents and run-down of ionic currents. 2. Depolarizing voltage clamp pulses from -40 mV elicited L-type Ca2+ current (ICa) that exhibited an initial rapid phase of inactivation followed by a secondary slower inward current component that decayed over about 100 ms. The secondary inward component appeared as a slowly decaying inward tail current following short (10-40 ms) depolarizing clamp steps. 3. Slowly decaying inward currents were abolished by internally dialysing pacemaker cells with 2 mM EGTA using a ruptured patch recording method. Inward tail currents were also abolished by exposure to 1 microM ryanodine and significantly decreased by replacing 85% of external Na+ with lithium, without effect on peak ICa. These findings identify a Na(+)-Ca2+ exchange current (INa-Ca) that is mediated by sarcoplasmic reticulum (SR) Ca2+ release. 4. Properties of INa-Ca and ICa differed significantly: (i) ICa exhibited a bell-shaped voltage dependence that peaked at 0 mV and decreased at more positive voltages. INa-Ca was maximal at -10 mV and remained relatively constant at more positive voltages; (ii) a paired pulse protocol showed that the time course of INa-Ca recovery (5 s) was significantly longer than that of ICa (2 s); (iii) cadmium (50 microM) induced an inhibition of ICa that did not correlate in time with changes in INa-Ca. 5. The duration of depolarizing steps between 10 and 120 ms had no effect on the time course of INa-Ca tail currents. 6. Isoprenaline > or = 5 x 10(-8) M significantly increased peak ICa amplitude, peak INa-Ca amplitude, accelerated INa-Ca rate of decay and decreased the absolute time of INa-Ca decay. 7. Free-running pacemaker action potentials were clamped during diastole at either -40 or -70 mV (maximum diastolic potential) for variable periods of time. At times between 0.2 and 1 s, INa-Ca exhibited a voltage-dependent increase in amplitude over time, i.e. INa-Ca recovered more rapidly from -70 mV than from -40 mV. At times > 2 s, INa-Ca exhibited a voltage-dependent decline in amplitude over time, i.e. from -40 mV INa-Ca decreased by 10% of maximum whereas from -70 mV INa-Ca decreased by 60% of maximum.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of isoprenaline on I(f) current in latent pacemaker cells isolated from cat right atrium: ruptured vs. perforated patch whole-cell recording methods

Whole-cell recording techniques were used to study the time-dependent inward current activated on hyperpolarization (I(f)) and its response to isoprenaline in latent atrial pacemaker cells isolated from cat right atrium. To determine whether the response to isoprenaline depended on the type of recording method, we analysed I(f) using either a standard ruptured-patch, or a nystatin-perforated-patch, whole-cell recording method. All cells beat rhythmically at 35 degrees C and exhibited normal pacemaker action potentials and I(f) current, regardless of the recording method. With the ruptured-patch method, pacemaker action potentials ceased activity within a few minutes and I(f) amplitude decreased "ran down" to 74% of control within 10 min of rupturing the patch. Isoprenaline (1 microM) elicited variable changes in I(f) amplitude among different latent pacemaker cells resulting in no net change in mean current amplitude (n = 6). In addition, isoprenaline failed to change the voltage dependence of the I(f) activation curve. On the other hand, using a nystatin-perforated-patch method, pacemaker action potentials and I(f) exhibited no significant changes over the same 10 min period. Under these conditions, isoprenaline consistently increased I(f) in all cells studied (+90%) at -80 mV; n = 8), and increased the spontaneous rate of pacemaker action potentials by 58 +/- 7% (n = 5). Moreover, isoprenaline elicited a significant positive shift (+11 mV) in the half-maximal activation voltage of the I(f) activation curve (n = 3). We conclude that latent atrial pacemakers consistently exhibit I(f) current, and that isoprenaline consistently elicits an increase in I(f) amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and experimental studies on shallow needling technique for treating childhood diarrhea

Treatment of diarrhea in children by shallow needling and by drugs was studied in 3 separate groups for comparison. For Group I, the lateral line II of the forehead was taken, i.e. the upper, middle and lower points of the line staring from Toulinqi (UB 15) vertically downwards to the place 1 cm below the hairline were selected. For Group II, shallow needling was done on body acupoints, the main points selected being Qihai (Ren 6), Shuifen (Ren 9), bilateral Tianshu (St 25), and bilateral Zusanli (St 36); the adjuvant acupoints were Taibai (Sp 3) and Gongsun (Sp 4). The depth of shallow needling was merely puncturing the skin. For Group III the drugs used were Liteling, Berberine, Gentamycin, Ampicillin, and SMZ Co. The results of treatment in Group I and II differed insignificantly, while both were significantly superior to drugs in Group III. Experimental studies also showed that shallow needling enhanced the humoral and cellular immunity and promoted the intestinal peristaltic function.

DNA damage and cell cycle regulation of ribonucleotide reductase

Ribonucleotide reductase (RNR) catalyzes the rate limiting step in the production of deoxyribonucleotides needed for DNA synthesis. In addition to the well documented allosteric regulation, the synthesis of the enzyme is also tightly regulated at the level of transcription. mRNAs for both subunits are cell cycle regulated and inducible by DNA damage in all organisms examined, including E. coli, S. cerevisiae and H. sapiens. This DNA damage regulation is thought to provide a metabolic state that facilitates DNA replicational repair processes. S. cerevisiae also encodes a second large subunit gene, RNR3, that is expressed only in the presence of DNA damage. Genetic analysis of the DNA damage response in S. cerevisiae has shown that RNR expression is under both positive and negative control. Among mutants constitutive for RNR expression are the general transcriptional repression genes, SSN6 and TUP1. Mutations in POL1 and POL3 also activate RNR expression, indicating that the DNA damage sensory network may respond directly to blocks in DNA synthesis. A protein kinase, Dun1, has been identified that controls inducibility of RNR1, RNR2 and RNR3 in response to DNA damage and replication blocks. This result suggests that the RNR genes in S. cerevisiae form a regulon that is coordinately regulated by protein phosphorylation in response to DNA damage.

Changes in the level of perforin and its transcript during effector and target cell interactions

Perforin is a cytoplasmic granule protein expressed in cytotoxic lymphocytes, and is capable of lysing target cells. This protein is induced as cytotoxic T cells are activated, and the mRNA expression is modulated by various stimulators. These observations suggest possible changes in the level of perforin transcripts and protein when killer lymphocytes meet specific target cells leading to target cell death. To address this question, we examined three murine T-cell clones and primary human NK cells in perforin expression. When the cytotoxic lymphocytes were exposed to sensitive targets, perforin mRNA disappeared within 5 to 30 min and appeared within an hour thereafter. Among the murine T cell clones, L3 and OE4 showed two phases of mRNA decrease while human NK cells and the third murine T cell clone, AB.1, showed only one phase of mRNA loss during a 240 min period. The data indicate that when cytotoxic lymphocytes receive signals from a sensitive target, the cells rapidly degrade previously accumulated perforin mRNA and synthesize new transcripts. Interestingly, heat shock protein 70 mRNA was induced as the perforin mRNA levels recovered, while P55 Il-2 receptor mRNA was downregulated within 5 min after exposure to targets. The perforin protein level also rapidly decreased immediately after the interaction with the target, followed by a recovery, and then another decrease as seen in primary human NK cells, OE4 and L3 cells. However, in the AB.1 clone, no change in perforin content was detectable, despite the loss of perforin mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

IDDM patients' sera recognize a novel 30-kD pancreatic autoantigen related to chymotrypsinogen

We have examined, by western immunoblot analysis, the sera of 16 insulin-dependent diabetes mellitus patients (IDDM) for the presence of autoantibodies against proteins extracted from islet-cell enriched preparations of normal human pancreata. A novel putative autoantigen recognized by late stage IDDM patients sera was identified, and its amino acid sequence was partially determined. Islets of Langerhans were partially purified by a modified collagenase digestion procedure, and subsequent protein extracts were fractionated by one-dimensional or two-dimensional polyacrylamide gel electrophoresis (1-D or 2-D SDS-PAGE). Immunoblot analysis revealed a 30-kD species which was recognized by 4 of 16 IDDM patients sera, but none of 16 normal sera. The 30-kD protein, appeared as a single band on 1-D SDS-PAGE, but was resolved on 2-D gel electrophoresis as several distinct protein species with different isoelectric points (pI's), ranging from 7 to 9. The amino terminal sequence of one such species was partially determined by microsequencing, and the second through the fourteenth amino acids were found to be identical to the corresponding sequence in human chymotrypsinogen. The fifteenth through the eighteenth amino acids were different from the known chymotrypsinogen sequence. This region corresponds with the site that is cleaved to activate chymotrypsinogen. Based on the size and sequence homology, this antigen appears to be related to chymotrypsinogen. We conclude that this 30-kD species may be an autoantigen in some late stage IDDM patients.

Pheromone-induced signal transduction in Saccharomyces cerevisiae requires the sequential function of three protein kinases

Protein phosphorylation plays an important role in pheromone-induced differentiation processes of haploid yeast cells. Among the components necessary for signal transduction are the STE7 and STE11 kinases and either one of the redundant FUS3 and KSS1 kinases. FUS3 and presumably KSS1 are phosphorylated and activated during pheromone induction by a STE7-dependent mechanism. Pheromone also induces the accumulation of STE7 in a hyperphosphorylated form. This modification of STE7 requires the STE11 kinase, which is proposed to act before STE7 during signal transmission. Surprisingly, STE7 hyperphosphorylation also requires a functional FUS3 (or KSS1) kinase. Using in vitro assays for FUS3 phosphorylation, we show that pheromone activates STE7 even in the absence of FUS3 and KSS1. Therefore, STE7 activation must precede modification of FUS3 (and KSS1). These findings suggest that STE7 hyperphosphorylation is a consequence of its activation but not the determining event.

MAP kinase-related FUS3 from S. cerevisiae is activated by STE7 in vitro

Pheromone-stimulated haploid yeast cells undergo a differentiation process that allows them to mate. Transmission of the intracellular signal involves threonine and tyrosine phosphorylation of the redundant FUS3 and KSS1 kinases, which are members of the MAP kinase family. FUS3/KSS1 phosphorylation depends on two additional kinases, STE11 and STE7 (refs 2, 5, 6). Genetic analyses predict an ordered pathway where STE11 acts before STE7 and FUS3/KSS1 (refs 2, 7). Here we report that STE7 is a dual-specificity kinase that modifies FUS3 at the appropriate sites and stimulates its catalytic activity in vitro. From these data and previous genetic results, we argue that STE7 is the physiological activator of FUS3. Recent indications that MAP kinase activators are related to STE7 suggest that signal transduction pathways in many, if not all, eukaryotic organisms use homologous kinase cascades.

Inducible T cell antigen 4-1BB. Analysis of expression and function

4-1BB is an inducible receptor-like protein expressed in both cytolytic and Th cells. Optimal induction of 4-1BB mRNA in T cells required both PMA and ionomycin stimulation, indicating that protein kinase C activation and increases in intracellular Ca2+ were required for its expression. 4-1BB was categorized as an early activation gene since the protein synthesis inhibitor, cycloheximide, blocked the induction of 4-1BB mRNA. A rat mAb, 53A2, was generated against recombinant soluble 4-1BB and was used to characterize this molecule. 4-1BB is a 30-kDa glycoprotein and appears to exist as both a monomer and a 55-kDa dimer on the cell surface of a T cell clone. The 4-1BB protein may be post-translationally modified since its predicted backbone is 25 kDa. FACS analysis indicated that 4-1BB was inducible and expressed on the cell surface of activated splenic T cells and thymocytes. Cross-linking of 4-1BB on anti-CD3-stimulated T cells with 53A2 resulted in a dramatic enhancement of T cell proliferation. This suggests that 4-1BB may function as an accessory signaling molecule during T cell activation.

Complex karyotypic abnormalities including t(8;22) in a patient with chronic lymphocytic leukemia

The case of a 49-year-old Chinese man with B-cell chronic lymphocytic leukemia (B-CLL) is presented. Complex karyotypic abnormalities comprising t(8;22)(q24;q11), trisomy 7, a deletion of 11q, and two small marker chromosomes were observed in PWM-stimulated cultures of his peripheral blood cells. To our knowledge, this is the first report of a t(8;22) in CLL.

Inducible T cell antigen 4-1BB. Analysis of expression and function

4-1BB is an inducible receptor-like protein expressed in both cytolytic and Th cells. Optimal induction of 4-1BB mRNA in T cells required both PMA and ionomycin stimulation, indicating that protein kinase C activation and increases in intracellular Ca2+ were required for its expression. 4-1BB was categorized as an early activation gene since the protein synthesis inhibitor, cycloheximide, blocked the induction of 4-1BB mRNA. A rat mAb, 53A2, was generated against recombinant soluble 4-1BB and was used to characterize this molecule. 4-1BB is a 30-kDa glycoprotein and appears to exist as both a monomer and a 55-kDa dimer on the cell surface of a T cell clone. The 4-1BB protein may be post-translationally modified since its predicted backbone is 25 kDa. FACS analysis indicated that 4-1BB was inducible and expressed on the cell surface of activated splenic T cells and thymocytes. Cross-linking of 4-1BB on anti-CD3-stimulated T cells with 53A2 resulted in a dramatic enhancement of T cell proliferation. This suggests that 4-1BB may function as an accessory signaling molecule during T cell activation.

Evaluation of 90:10 poly(D,L-lactide-co-glycolide) microspheres containing norethisterone: drug release and biodegradation

Poly(D,L-lactide-co-glycolide) (PLG, 90:10) microspheres containing 20% norethisterone (NET) were prepared by solvent evaporation method. Microspheres in the size ranges of 65 to 100 microns were sterilized by irradiation and used for further study. In vitro release showed fairly constant release of NET from the above microspheres over more than 90 days. However, in vivo drug release determined by residual NET analysis after i.m. injection in rats indicated a faster release rate. About 95% of NET was released in a period of 45 days. At the dose of 80 mg of microspheres, vaginal estrus cycles were inhibited for 45 days compared to 27 days for the same dose of NET crystals in rats. Biodegradation of the microspheres was tested by direct measurement of molecular weight losses and SEM observation of morphological changes of the microspheres, which showed continuous erosion in the internal matrix of microspheres with the decrease of molecular weight of PLG until total collapse of microspheres, and biodegradation was faster in rats than in human serum at 37 degrees C in vitro. Total degradation of 90:10 PLG microspheres was less than 7 months in rats and more than 9 months in vitro.

Mesangioproliferative glomerulonephritis in mink with encephalitozoonosis

Renal specimens from 6 mink with encephalitozoonosis were studied by light and electron microscopy and immunohistochemistry. The glomeruli of affected kidneys had a mesangioproliferative glomerulonephritis which was characterized by an increase in mesangial cells and matrix in most glomeruli. Some glomeruli were partially or completely sclerosed. There were protein or granular casts in the cortical and medullary tubules. Interstitial nephritis, vasculitis and tubular cysts were found. Electron microscopy demonstrated extensive matrix and increased cellularity in the mesangial areas. Glomeruli showed segmentally thickened or wrinkled capillary basement membranes. Electron dense deposits were found in the glomerular basement membranes and mesangium. Peroxidase-anti-peroxidase immunohistochemistry demonstrated that IgG and IgM positive material was present as granular deposits in the glomerular basement membrane and occasionally in the mesangium.

Molecular genetics of human androgen insensitivity

Androgen insensitivity syndromes represent one cause of human male pseudohermaphroditism related to defects in the androgen receptor. The formation of a biologically active androgen receptor complex with testosterone and 5 alpha-dihydrotestosterone is required for normal androgen action during fetal development and differentiation of the internal accessory sex glands and external genitalia. Cloning of the human androgen receptor complementary DNA and genetic screening of human subjects with the clinical and biochemical features of androgen insensitivity using the polymerase chain reaction, denaturing gradient gel electrophoresis and nucleotide sequencing techniques have led to the identification of molecular defects in the androgen receptor. The complexity of phenotypic presentation by affected subjects with the complete or partial forms of androgen insensitivity is represented by the heterogeneity of androgen receptor gene mutations which include deletions and point mutations, with the latter causing inappropriate splicing of RNA, premature termination of transcription and amino acid substitutions. The naturally occurring mutations in the androgen receptor of subjects with androgen insensitivity represent a base upon which we can increase our understanding of the structure and function of the androgen receptor in normal physiology and disease.

The gene for human eosinophil Charcot-Leyden crystal protein directs expression of lysophospholipase activity and spontaneous crystallization in transiently transfected COS cells

Expression of the gene encoding human eosinophil lysophospholipase, the Charcot-Leyden crystal (CLC) protein, was studied in transiently transfected COS cells. Recombinant CLC (rCLC) protein expression was demonstrated both by Western blot and radioimmunoassay inhibition analyses of transfected COS cell extracts and by immunofluorescent staining and ultrastructural immunogold analyses of intact cells. The rCLC protein was immunochemically indistinguishable from native eosinophil-derived CLC protein, and each transfected COS cell expressed approximately 11 pg of rCLC protein as determined by radioimmunoassay and assessment of transfection efficiency. Immunofluorescent microscopy and ultrastructural immunogold analyses localized rCLC protein to the nucleus, cytoplasm, and plasma membrane of COS cells. Lysates from transfected COS cells producing CLC protein expressed significant lysophospholipase activity. Furthermore, rCLC protein expressed in COS cells spontaneously formed the distinctive intracytoplasmic and intranuclear hexagonal bipyramidal crystals characteristic of the native eosinophil and basophil-derived protein. Expression of the CLC gene confirms the authenticity of the CLC cDNA, the expression of lysophospholipase activity by this unique eosinophil and basophil constituent, and will facilitate the routine purification of the active enzyme for in vitro and animal model studies of its role (or roles) in eosinophil and basophil associated allergic inflammation and eosinophil-parasite interactions.

Abolition with chloramine-T of inactivation in barnacle muscle fibers results in stimulation of the ouabain-insensitive sodium efflux

The hypothesis that chloramine-T stimulates the basal Na+ efflux in barnacle fibers as the result of the entry of trigger Ca2+ into the myoplasm from the bathing medium was examined in this study. Two reasons for doing so can be given. One is that the oxidant is known to abolish inactivation in sodium and potassium channels. The other is that L-type Ca2+ channels are present in barnacle fibers, and an increase in internal free Ca2+ in these fibers is known to stimulate the Na+ efflux, particularly in ouabain-poisoned fibers. The results of the experiments are as follows: (i) Chloramine-T exerts a biphasic effect on the Na+ efflux: inhibition is followed by stimulation, the threshold concentration being 10(-5) M. This is also found to be the threshold concentration for shortening of these fibers. (ii) The kinetics of the inhibitory effect resemble those of ouabain. (iii) Ouabain is without effect on the stimulatory phase caused by chloramine-T. (iv) Application of chloramine-T after the full effect of 10(-4) M-ouabain is reached elicits solely a stimulatory response. (v) The dose-response curves for the stimulatory action of chloramine-T in unpoisoned and ouabain-poisoned fibers are alike except that the threshold concentration is less than 10(-5) M in poisoned fibers. (vi) Basal light emission from unpoisoned and ouabain-poisoned fibers loaded with the photoprotein, aequorin, some 60 min beforehand increases as soon as they are exposed to 10(-4) M chloramine-T. The response recorded in unpoisoned fibers is monophasic and usually transitory, whereas it is multiphasic and usually sustained in ouabain-poisoned fibers. (vii) The dose-response curve for chloramine-T shows a shift to the left in poisoned fibers. (viii) The magnitude of the rise in light emission depends on the external Ca2+ concentration. A rise fails to take place in the nominal absence of external Ca2+. Taken together, these results support the above hypothesis that chloramine-T causes the entry of trigger Ca2+ into the myoplasm from the outside and provide evidence that stimulation of the Na+ efflux is associated not only with this event but also with a reduced Na+ gradient resulting from inhibition of the membrane Na+/K(+)-ATPase system by the oxidant. Thus, the suggestion put forward is that this oxidant promotes reverse Na+/Ca2+ exchange and is able to exert multiple effects on membrane transport.

[An epidemiological investigation of outbreak of measles among temporarily living people in Shenyang]

This paper reported an outbreak of measles occurred in a factory of Heping District in Shenyang in March 1989. All of the six diagnosed cases were temporarily workers, which represented 15 percent (6/40) of total workers. No secondary cases were detected. The results of epidemiological and laboratory analysis showed that this outbreak was caused by an imported case, and only spread in temporarily workers. Furthermore, we discussed that under the condition that measles incidence was limited under control level, even imported cases could not cause epidemic of measles. So, it is indicated that the flowing people can easily cause accumulation of susceptible people in cities, which may result in outbreak of some infectious diseases.

Influence of recombinant human interleukin (IL)-7 on disease progression in mice infected with Friend virus complex

Recombinant human (rhu) IL-7 was evaluated for its influence on disease progression in mice infected with the polycythemia-inducing strain of the Friend virus complex (FVC). DBA/2 mice were injected i.v. with FVC, and then treated s.c. with rhuIL-7. IL-7 significantly prolonged survival time and decreased spleen focus-forming virus (SFFV) levels, expression of SFFV mRNA and SFFV protein production in FVC-infected mice. IL-7 did not appear to directly inactivate SFFV. Although both splenic weight and cellularity in FVC-infected mice treated with IL-7 were higher than those of normal mice, they were respectively 58% and 66% lower than those of the untreated FVC-infected mice. NK-cell activity was substantially lower in FVC-infected mice than in normal mice, while IL-7 restored NK-cell activity to normal levels. IL-6 and IFN-gamma levels were markedly reduced in FVC-infected mice compared to normal mice, but treatment of FVC-infected mice with IL-7 restored these cytokine levels. While the actual mechanisms of these effects are not yet known, the results suggest the potential therapeutic efficacy of IL-7 for certain hematopoietic and viral disorders, possibly mediated through an action on accessory cells and cytokine production.

Isolation of crt mutants constitutive for transcription of the DNA damage inducible gene RNR3 in Saccharomyces cerevisiae

Ribonucleotide reductase is an essential enzyme that catalyzes the rate limiting step for production of the deoxyribonucleotides required for DNA synthesis. It is encoded by three genes, RNR1, RNR2 and RNR3, each of which is inducible by agents that damage DNA or block DNA replication. To probe the signaling pathway mediating this DNA damage response, we have designed a general selection system for isolating spontaneous trans-acting mutations that alter RNR3 expression using a chromosomal RNR3-URA3 transcriptional fusion and an RNR3-lacZ reporter plasmid. Using this system, we have isolated 202 independent trans-acting crt (constitutive RNR3 transcription) mutants that express high levels of RNR3 in the absence of DNA damaging agents. Of these, 200 are recessive and fall into 9 complementation groups. In some crt groups, the expression of RNR1 and RNR2 are also elevated, suggesting that all three RNR genes share a common regulatory pathway. Mutations in most CRT genes confer additional phenotypes, among these are clumpiness, hydroxyurea sensitivity, temperature sensitivity and slow growth. Five of the CRT genes have been identified as previously cloned genes; CRT4 is TUP1, CRT5 is POL1/CDC17, CRT6 is RNR2, CRT7 is RNR1, and CRT8 is SSN6. crt6-68 and crt7-240 are the first ts alleles of RNR2 and RNR1, respectively, and arrest with a large budded, cdc terminal phenotype at the nonpermissive temperature. The isolation of crt5-262, an additional cdc allele of POL1/CDC17, suggests for the first time that directly blocking DNA replication can provide a signal to induce the DNA damage response. crt2 mutants show a defect in basal level expression of RNR1-lacZ reporter constructs. These are the first mutants isolated in yeast that alter the regulation of DNA damage inducible genes and the identification of their functions sheds light on the DNA damage sensory network.

Ribonucleotide reductase: regulation, regulation, regulation

Ribonucleotide reductase (RNR) catalyses the rate limiting step in the production of deoxyribonucleotides needed for DNA synthesis. It is composed of two dissimilar subunits, R1, the large subunit containing the allosteric regulatory sites, and R2, the small subunit containing a binuclear iron center and a tyrosyl free radical. Recent isolation of the mammalian and yeast RNR genes has shown that, in addition to the well documented allosteric regulation, the synthesis of the enzyme is also tightly regulated at the level of transcription. The mRNAs for both subunits are cell-cycle regulated and, in yeast, inducible by DNA damage. Yeast encode a second large subunit gene, RNR3, that is expressed only in the presence of DNA damage. This regulation is thought to provide a metabolic state that facilitates DNA replicational repair processes.