Costimulation by B7 modulates specificity of cytotoxic T lymphocytes: a missing link that explains some bystander T cell activation

It has been proposed that some bystander T cell activation may in fact be due to T cell antigen receptor (TCR) cross-reactivity that is too low to be detected by the effector cytotoxic T lymphocyte (CTL). However, this hypothesis is not supported by direct evidence since no TCR ligand is known to induce T cell proliferation and differentiation without being recognized by the effector CTL. Here we report that transgenic T cells expressing a T cell receptor to influenza virus A/NT/68 nucleoprotein (NP) 366-374:Db complexes clonally expand and become effector CTLs in response to homologous peptides from either A/PR8/34 (H1N1), A/AA/60 (H2N2), or A/NT/68 (H3N2). However, the effector T cells induced by each of the three peptides kill target cells pulsed with NP peptides from the H3N2 and H2N2 viruses, but not from the H1N1 virus. Thus, NP366-374 from influenza virus H1N1 is the first TCR ligand that can induce T cell proliferation and differentiation without being recognized by CTLs. Since induction of T cell proliferation was mediated by antigen-presenting cells that express costimulatory molecules such as B7, we investigated if cytolysis of H1N1 NP peptide-pulsed targets can be restored by expressing B7-1 on the target cells. Our results revealed that this is the case. These data demonstrated that costimulatory molecule B7 modulates antigen specificity of CTLs, and provides a missing link that explains some of the bystander T cell activation.

[Separation and determination of metsulfuron, bensulfuron, acetochlor by high performance liquid chromatography]

In this paper a high performance liquid chromatographic method for the separation and determination of metsulfuron, bensulfuron and acetochlor in the composite herbicide "Nongjiayi" is described. The concentration of methanol in the mobile phase and the temperature of the column affected the k' factor and the separation of the three active ingredients. Impurities in the "Nongjiayi" did not interfere with the determination. Chromatographic conditions were Shim-Pack CLC-C8 (150 mm x 6 mm i.d., 5 microm), mobile phase of methanol-water (60:40, V/V) and UV detector at 240 nm. Quantification was carried out with the three external standards. The average recovery was 98.81% with RSD=0.80% for metsulfuron, 99.10% with RSD=0.78% for bensulfuron and 99.72% with RSD=0.69% for acetochlor. The linear range of this method was 0.10-0.40 microg (r=0.9994) for metsulfuron, 0.40-1.60 microg (r=0.9995) for bensulfuron and 10-40 microg (r=0.9987) for acetochlor. The method is accurate, rapid and reproducible and can be applied to quality control for the "Nongjiayi".

Inhibitory effects of vinpocetine on sodium current in rat cardiomyocytes

AIM

To study the effects of vinpocetine (Vin) on the sodium current (INa) in cardiomyocytes.

METHODS

The sodium current in adult rat ventricular myocytes was measured by whole cell patch-clamp technique.

RESULTS

The INa in cardiomyocytes was blocked reversibly by Vin, in concentration-dependent and voltage-dependent manner, but not rate- or use-dependent. The INa was attenuated by 13%-75% when the Vin concentration was raised from 10 to 80 mumol.L-1. The IC50 (95% confidence limits) was 36.4 (28.1-47.1) mumol.L-1. When the membrane potential depolarized over the range of -90 mV to +40 mV in 10-mV step, inhibitory effect of Vin on the INa was 39% at first, then maintained at a higher level, about 52% +/- 5%. The maximal depression (57%) reached at about 0 mV. Vin influenced both the activation and inactivation processes of sodium channel, and resulted in attenuation of the window currents (the slowly inactivating sodium currents).

CONCLUSION

Vin inhibited sodium currents in rat ventricular myocytes.

Natural antisense RNA/target RNA interactions: possible models for antisense oligonucleotide drug design

Current antisense oligonucleotides designed for drug therapy rely on Watson-Crick base pairing for the specificity of interactions between antisense and target molecules. However, thermodynamically stable duplexes containing non-Watson-Crick pairs have been formed with synthetic oligonucleotides. There are also numerous examples of non-canonical base pairs that participate in stable intra- and inter-molecular RNA/RNA pairing in prokaryotic and eukaryotic cells. Several natural antisense RNA/target RNA duplexes contain looped-out and bulged positions as well as non-canonical pairs as exemplified by formation of the Escherichia coli antisense micF RNA/ompF mRNA duplex. Secondary structures and the phylogenetic conservation of nucleotide sequences are well characterized in this system. Natural antisense/ target interactions may serve as models for determining possible and optimal antisense/target interactions in oligonucleotide drug design.

Characterization of dopamine-induced depolarization of prefrontal cortical neurons

Dopamine (DA) has been reported to depolarize neurons in the prefrontal cortex (PFC). To further characterize this effect of DA, we made whole cell recordings from PFC pyramidal cells in rat brain slices. As reported previously, DA depolarized most PFC cells tested. This effect of DA was concentration-dependent and persisted in the presence of synaptic blockade, indicating a direct effect of DA on the recorded cell. During DA-induced depolarization, PFC neurons consistently showed an increase in excitability, suggesting that the depolarization is not directly related to DA-induced inhibition of PFC neurons previously observed in vivo. Surprisingly, the effect of DA was not mimicked or blocked by several commonly used DA agonists and DA antagonists. The alpha and beta antagonists phentolamine and alprenolol and the atypical antipsychotic drug clozapine also showed no significant effect on DA-induced depolarization. These results suggest that DA-induced depolarization may be mediated by a nonspecific mechanism. However, it remains possible that there exists a new type of DA receptors in the PFC not sensitive to classical DA agonists and antagonists, particularly given the fact that DA applied in the same manner depolarized only PFC neurons but not those in the striatum or the substantia nigra.

Vitamin E inhibits apoptosis, DNA modification, and cancer incidence induced by iron-mediated peroxidation in Wistar rat kidney

We have developed an experimental model of iron-induced oxidative nephrotoxicity and renal cancer. Using this model, the effect of vitamin E, a known antioxidant, was investigated. Three-week-old male Wistar rats were fed with vitamin E-sufficient (control) and vitamin E-supplemented diets throughout the experiment. After 1 month of feeding, iron-induced tissue lipid peroxidation, apoptosis, and formation of 8-hydroxydeoxyguanosine, a known DNA oxidative modification, were observed by cold Schiff staining, in situ labeling method (staining by terminal deoxynucleotidyl transferase-mediated nick end labeling), and high-performance liquid chromatography with electrochemical detection system, respectively, in the groups of rats treated with ferric nitrilotriacetate (Fe-NTA; Fe, 10 mg/kg body weight). For the vitamin E intervention study on Fe-NTA-induced renal carcinogenesis, two groups of rats fed vitamin E-sufficient and vitamin E-supplemented diets (30 and 20 rats, respectively) were treated with Fe-NTA (Fe, 7.5 mg/kg body weight once or twice a week) i.p. for 3 months and observed for 9 additional months. Five of the vitamin E-sufficient rats died during the first 3-month period. The results showed that vitamin E could inhibit tissue lipid peroxidation, apoptosis, 8-hydroxydeoxyguanosine formation, and the development of cancer [11 of 25 rats (44%) for vitamin E-sufficient versus 1 of 20 rats (5%) for vitamin E-supplemented rats, respectively]. These studies strongly suggest that in Fe-NTA-induced renal cancer, as with certain other types of cancer, oxidative stress plays an important role in carcinogenesis, and an antioxidant is an effective chemopreventive measure.

CTLA-4-B7 interaction is sufficient to costimulate T cell clonal expansion

T cell costimulation, particularly by the B7 family members B7-1 and B7-2, plays a critical role in regulating T cell-mediated immunity. Two molecules on T cells, CD28 and CTLA-4, are known to bind to B7. It has been suggested that CD28-B7 interaction promotes T cell response, whereas B7-CTLA-4 interaction downregulates T cell clonal expansion. However, the proposed responses of individual receptors to B7 have not been verified directly. Here, we report that B7-1 promotes clonal expansion of CD28-deficient T cells, and that the CD28-independent costimulatory activity is mediated by CTLA-4, as it is completely blocked by intact and Fab of anti-CTLA-4 mAb. In addition, a mutant B7-1 molecule, B7W88 >A, which has lost binding to CD28 but retained significant CTLA-4 binding activity, promotes T cell clonal expansion. Furthermore, while presence of CD28 enhances T cell response to B7-1, such response is also completely blocked by anti-CTLA-4 mAb. Taken together, our results demonstrate that B7-CTLA-4 interaction promotes T cell clonal expansion, and that optimal T cell response to B7 is achieved when both CD28 and CTLA-4 interact with B7. These results establish an important function of CTLA-4 in promoting T cell activation, and suggest an alternative interpretation of the function of CTLA-4 in T cell activation.

Electrophysiological effects of felodipine on guinea pig papillary muscles

AIM

To determine whether felodipine (Fel) has Ca2+ channel blocking effect in mammalian myocardium in comparison with those of nifedipine (Nif) and verapamil (Ver).

METHODS

The action potentials (AP), the slow AP and the inward slow Ca2+ currents of guinea pig papillary muscles were studied using intracellular microelectrodes and voltage-clamp techniques.

RESULTS

Fel 1, 3, and 10 mumol.L-1 concentration-dependently shortened APD30, APD50, and APD90 of the AP, while Vmax and APA were not affected. The effect of Fel was not reversible on washout. At 0.1, 1, 3, and 10 mumol.L-1, Fel depressed Vmax, APA, APD30, APD50, and APD90 of the slow AP in a dose-dependent manner. The inward slow Ca2+ currents were reduced by Fel 3 mumol.L-1. APD30, APD50, and APD90 of the first AP after rest were still shortened by Fel. When the stimulation frequency was elevated, the effect of Fel on the AP and slow AP decreased. The effect of Fel 3 mumol.L-1 on the slow AP was abolished in preparation pretreated with trifluoperazine. The threshold concentrations of Nif and Ver for the inhibition of APD50 of the slow AP (P < 0.05) were 0.1 and 1 mumol.L-1, respectively. The effect of Ver 3 mumol.L-1 on the fast AP was not reversible on washout, but that of Nif 3 mumol.L-1 was. When the stimulation frequency was elevated from 0.5 to 2 Hz, the effect of Nif 3 mumol.L-1 on the fast AP was reduced, but that of Ver 3 mumol.L-1 was increased.

CONCLUSION

Fel inhibited mainly the resting state of the cardiac Ca2+ channel. The potency of Fel was about the same as that of Nif and about 10 times more potent than that of Ver.

[Comparison of human papilloma virus-DNA in condyloma acuminatum, cervical cancer and the female genital tract]

OBJECTIVE

To examine human papilloma virus (HPV) infection rate and types in several lesions of the genital tract and to observe the relation between HPV and host cells for differential handling of cases and for early diagnosis.

METHODS

Tissues from 89 cases of condyloma acuminata, 76 cases of cervical cancer and swabs from 198 cases of normal vaginal were analysed by polymerase chain reaction for HPV infective rate. Main HPV types were compared and Southern blot was used to compare the physical pattern of HPV in condyloma acuminata and cervical cancer.

RESULTS

The positive rates of HPV-DNA in condyloma acuminata and cervical cancer were respectively 98.9% and 94.7%. The primary types of the former were HPV 6, 11 and of the latter mainly 16 and 18. The latent infective rates in normal vagina was 37.4%, among which, HPV 6, 11, 16, 18 consisted of only 21.6%. HPV11-DNA in condyloma acuminata existed mainly in episodic form. Most of HPV16-DNA in cervical cancer integrates into the host cells with variation.

CONCLUSIONS

The different types of HPV are related to particular morphology and characteristics of lesions. The relation of HPV-DNA to host cell and can offer some reference for the determination of the character of the lesion, and it may be award of malignant transformation.

[The changing trend of cesarean section rates in 35 years]

OBJECTIVE

To investigate the changing trend of cesarean section rates in 35 years.

METHODS

Samples taken from 4 months (March, June, September, December) of a year every 5 years in 35 years (from 1959 to 1994) were analysed and a total of 1 667 cases were collected.

RESULTS

Cesarean section rates increased since 1975 and particularly from 1980 to 1994. The causes of this trend may be related to following reasons. (1) Improvement of skill and safety of operation. (2) Change of indications of cesarean section. (3) Social factors.

CONCLUSION

The decrease of perinatal mortality rate was not relevant only to the cesarean section rate, but dependent more on good perinatal care.

Ginseng extract scavenges hydroxyl radical and protects unsaturated fatty acids from decomposition caused by iron-mediated lipid peroxidation

This study was conducted to investigate whether or not the antioxidation effect of ginseng extract directly inhibits decomposition of unsaturated fatty acid caused by iron and hydrogen peroxide-induced lipid peroxidation, and whether this effect involves a hydroxyl radical-scavenging mechanism. Thiobarbituric acid-reactive substances (TBARS), gas chromatography, and electron spin resonance (ESR) spectrometer were used to measure lipid peroxidation, unsaturated fatty acid, and hydroxyl radical. The results showed TBARS formed and the loss of arachidonic acid during lipid peroxidation, and that hydroxyl radical formed by the Fenton reaction were completely inhibited by ginseng extract. This antioxidant effect of ginseng may be responsible for its wide pharmacological actions in clinical practice by a free radical reaction-inhibition mechanism.

Relationship between ornithine decarboxylase and cytoskeletal organization in cultured human keratinocytes: cellular responses to phorbol esters, cytochalasins, and alpha-difluoromethylornithine

Changes in cell shape occur during the cell cycle and influence cell proliferation and differentiation. In order to study how altered cell proliferation and cell shape are interrelated, we have studied ornithine decarboxylase (ODC) regulation in cultured normal human epidermal keratinocytes (NHEK). Cytoskeletal disruptors have been reported to modulate regulation of ODC; the products of ODC, the polyamines, influence actin polymerization rates in vitro, and polyamine auxotrophs have profoundly disrupted cytoskeletons. Therefore, altered ODC levels could be involved in signaling changes in cell shape and an intact cytoskeleton could transduce signals to regulate ODC levels. We had previously observed that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), which profoundly alters cell shape, markedly suppresses ODC biosynthesis in NHEK solely at posttranscriptional/protein synthesis levels. TPA treatment caused NHEK to rapidly assume a rounded morphology that was accompanied by a change in actin organization, as determined by rhodamine-phalloidin labeling. Immunolocalization of ODC showed a perinuclear/nuclear distribution in untreated NHEK and a more diffuse pattern after TPA treatment that was apparent within 15-30 min. Changes in ODC enzyme activity are not significant until 60 min after TPA treatment. NHEK treated with cytochalasin B or D to inhibit actin polymerization exhibited a diffuse ODC localization that could be reversed by removal of the cytochalasin; inhibition of ODC by alpha-difluoromethylornithine caused a diffuse ODC localization. All treatments resulted in cytoskeletal remodeling. These data are the first evidence for a distinct subcellular localization for ODC and suggest that changes in ODC localization may be an initial step in regulation of ODC activity. Furthermore, changes in ODC activity cause an altered cytoskeleton, suggesting one means by which growth regulatory signals can be transduced to the cytoskeleton from various signaling pathways.

Effects of toquipidine on ionic channels of cultured embryonic Xenopus laevis myoblasts and neurons

AIM

To study the effects of toquipidine (1-p-methyl-phenyl-2-(alpha-piperidinoacetyl)-1, 2, 3, 4-tetrahydroisoquinoline hydrochloride, Toq), a new anti-arrhythmic agent first synthesized in China, on ionic channels.

METHODS

Ionic channel currents were recorded by whole-cell patch clamp technique in cultured embryonic Xenopus laevis myoblasts and neurons.

RESULTS

Toq (0.1, 1, 10, and 100 mumol L-1) caused a concentration-dependent inhibition of the Na+ currents with IC50 7.2 mumol L-1 (5.3-9.8 mumol L-1). Toq (10 mumol L-1) also suppressed the high-voltage-activated Ca2+ currents in neurons. But the steady-state outward K+ currents in myoblasts were activated by Toq (10 mumol L-1).

CONCLUSION

Toq blocked the Na+ and Ca2+ channels and opened the steady-state outward K+ channels.

Photoirritation: a new photobiologic phenomenon induced by long wavelength UVA radiation in hairless mice treated with broad-spectrum sunscreens

While assessing the protective effect of broad-spectrum sunscreens against chronic UVA radiation, we observed a paradoxical worsening of skin damage with one product. To further examine this finding, five proprietory broad-spectrum sunscreens were applied to albino hairless mice irradiated thrice weekly for 32 weeks with a UVASUN lamp (> 340 nm). Appropriate age-matched controls were included. After approximately 12 weeks, two sunscreens induced a marked dermatitis. Biopsies showed damage greatly exceeding that found in UVA-irradiated, unprotected controls. Histologically, elastic fibers were hyperplastic, coalescing into elastotic clumps. Glycosaminoglycans also increased. Collagen damage was notable since UVA alone does not induce a histologic change. Electron microscopy confirmed these findings. Two other sunscreens provided nearly complete protection. Against chronic UVB radiation, the two UVA photoirritating sunscreens provided substantial protection. Since the UVA sunfilter, oxybenzone, was the same in all sunscreens, we postulate that an irritating component of the vehicle was responsible for the UVA-induced photoirritation. The fifth sunscreen produced severe damage with UVB and UVA.

Secondary structures of Escherichia coli antisense micF RNA, the 5'-end of the target ompF mRNA, and the RNA/RNA duplex

The Escherichia coli micF RNA is a prototype for a class of antisense RNAs encoded by genes at different loci from those that code for their target RNAs. RNAs in this class exhibit only partial complementarity to their targets. micF RNA binds to and regulates the stability of ompF mRNA in response to a variety of environmental stimuli. The secondary structures of micF RNA, ompF-213 mRNA (a segment containing the 213 nucleotides at the 5'-terminus of the target message), and the micF RNA/ompF-213 mRNA duplex were analyzed in vitro by partial digestion with structure-specific ribonucleases and chemical modification. Both micF RNA and ompF mRNA have single-stranded 5'-ends and contain stable stem-loop structures. Strong phylogenetic support for the proposed secondary structure for E. coli micF RNA is provided by a comparison of structural models derived from micF sequences from related bacteria. The micF RNA/ompF-213 mRNA duplex interaction appears to involve only a short segment of micF RNA. Unfolding of only one stem-loop of micF RNA and a minor stem-loop of ompF-213 mRNA appears to be necessary to form the duplex. The probing data suggest that the Shine-Dalgarno sequence and AUG start codon of ompF mRNA, found in single-stranded regions in the free message, are base-paired to micF RNA in the RNA/RNA duplex.

[Influence of different processing methods of four alkaloid contents in Strychnos nux-vomica L]

The contents of four alkaloids in different processed products of Strychnos nux-vomica hamely, vomicine, icajine, strychnine N-oxide and brucine N-oxide, were determined by TLC-densitometry. The relationship between alkaloid contents and processing methods was studied.

[Analgesic effect and toxicity of 3,15-diacetylbenzoylaconine and comparison with its analogues]

3, 15-Diacetylbenzoylaconine (Dia) is a new aconite alkaloid derivative. The analgesic ED50 (95% confidence limit) of sc Dia measured with the HAc-induced writhing method, hot-plate method and electric stimulation method in mice were 2.76 (2.34-3.26), 3.50 (2.69-4.54), and 4.20 (3.72-4.73) mg.kg-1, respectively. With the hot-plate method and tail flick method in rats, the analgesic ED50 of ip Dia were 2.75 (2.28-3.31) and 5.24 (4.35-6.31) mg.kg-1, respectively. The LD50 of sc Dia in mice and ip Dia in rats were 21.68 (17.25-27.25) and 10.96 (8.24-14.56) mg.kg-1, respectively. The magnitude of the analgesic therapeutic indices of Dia, 3-acetylaconitine (Ace) and aconitine (Aco) in all the above-mentioned algo-model were in the order of Dia > Ace > Aco. When they were injected iv at 0.1 ml.min-1 in rats, the doses of Dia, Ace, and Aco producing arrythmia were 3.3, 0.8, and 0.5 times as large as those producing analgesia while those of Dia, Ace, and Aco inducing respiratory inhibition were 3.9, 0.5 and 0.3 times, respectively. The magnitudes of the oil/water distribution coefficients with two method and the quotient ED50 icv/ED50 sc of Dia and Ace were > Aco.

Muscarinic stimulation of arachidonic acid release and prostaglandin synthesis in bovine ciliary muscle: prostaglandins induce cyclic AMP formation and muscle relaxation

In the present study it is demonstrated that in bovine ciliary muscle, muscarinic stimulation results in: (a) release of 14C-arachidonic acid (14C-AA) and 14C-labeled prostaglandins (PGs) from muscle prelabeled with 14C-AA; (b) release of endogenous PGs, measured by means of radioimmunoassay; (c) enhanced IP3 production and (d) muscle contraction. In addition, PGs, such as PGE2 and PGD2, increased cAMP formation and induced muscle relaxation. The studies on the kinetics of 14C-AA metabolism revealed that incorporation of 14C-AA into glycerolipids and its conversion into PGs by the ciliary muscle were rapid and time-dependent. The amounts of 14C-radioactivity recovered in the major PGs decreased in the following order: PGD2 > PGE2 < PGF2 alpha > 6-keto-PGF1 alpha. The rate of endogenous PGF2 alpha synthesis by iris-ciliary body tissues from different mammalian species was found to be in the following order: ciliary muscle < ciliary processes < sphincter muscle. The EC50s for muscarinic-stimulated release of 14C-AA, 14C-labeled PGs, and endogenous PGF2 alpha and PGE2, and for IP3 production and contraction of the ciliary muscle indicate that CCh is 2-16 times as potent as pilocarpine in eliciting these responses, with the greatest difference being for contraction. The maximal increase in ciliary muscle tension due to CCh was 48% greater than that evoked by pilocarpine. All PGs tested, including PGE2, 17-phenyl trinor PGE2, 11-deoxy PGE1, PGF2 alpha and PGD2 had no effect on IP3 production and contraction in the ciliary muscle. However, PGE2 and PGD2 stimulated cAMP formation and inhibited CCh-induced IP3 production in a dose-dependent manner. In addition, PGE2 and PGD2 induced relaxation in ciliary muscle precontracted by CCh. In presence of indomethacin (1 microM), the CCh-induced contraction was greater than that observed in absence of the cyclo-oxygenase inhibitor. It is suggested that in the ciliary muscle certain PGs, such as PGE2 and PGD2, may function to modulate, via cAMP, the responses to muscarinic stimulation in this tissue.

[Sites of analgesic action of 3,15-diacetylbenzoylaconine]

In the rat hot plate test, vocalization induced by electric stimulation, tail flick test, and the mouse acetic acid writhing test, 3, 15-diacetylbenzoylaconine (DABA) ip exhibited a dose-dependent analgesic activity. Intrathecally (ith) administered DABA (527, 1186 micrograms.kg-1) had no analgesic action. Microinjection of DABA 35-75 micrograms.kg-1 or 20 micrograms into the cerebral ventricle (icv) or the periaqueductal gray (PAG) exerted a remarkable analgesic activity, which was abolished after bilateral lesions of locus coeruleus (LC). Microinjection of DABA (20 micrograms) into LC failed to produce apparent analgesic action. These results suggested that the sites of analgesia of DABA were mainly at the central supraspinal structures, and PAG was one of the primary sites, while LC was one of the intermediate links.

SPK1 is an essential S-phase-specific gene of Saccharomyces cerevisiae that encodes a nuclear serine/threonine/tyrosine kinase

SPK1 was originally discovered in an immunoscreen for tyrosine-protein kinases in Saccharomyces cerevisiae. We have used biochemical and genetic techniques to investigate the function of this gene and its encoded protein. Hybridization of an SPK1 probe to an ordered genomic library showed that SPK1 is adjacent to PEP4 (chromosome XVI L). Sporulation of spk1/+ heterozygotes gave rise to spk1 spores that grew into microcolonies but could not be further propagated. These colonies were greatly enriched for budded cells, especially those with large buds. Similarly, eviction of CEN plasmids bearing SPK1 from cells with a chromosomal SPK1 disruption yielded viable cells with only low frequency. Spk1 protein was identified by immunoprecipitation and immunoblotting. It was associated with protein-Ser, Thr, and Tyr kinase activity in immune complex kinase assays. Spk1 was localized to the nucleus by immunofluorescence. The nucleotide sequence of the SPK1 5' noncoding region revealed that SPK1 contains two MluI cell cycle box elements. These elements confer S-phase-specific transcription to many genes involved in DNA synthesis. Northern (RNA) blotting of synchronized cells verified that the SPK1 transcript is coregulated with other MluI box-regulated genes. The SPK1 upstream region also includes a domain highly homologous to sequences involved in induction of RAD2 and other excision repair genes by agents that induce DNA damage. spk1 strains were hypersensitive to UV irradiation. Taken together, these findings indicate that SPK1 is a dual-specificity (Ser/Thr and Tyr) protein kinase that is essential for viability. The cell cycle-dependent transcription, presence of DNA damage-related sequences, requirement for UV resistance, and nuclear localization of Spk1 all link this gene to a crucial S-phase-specific role, probably as a positive regulator of DNA synthesis.