Neuropilin is a receptor for the axonal chemorepellent Semaphorin III

Extending axons in the developing nervous system are guided to their targets through the coordinate actions of attractive and repulsive guidance cues. The semaphorin family of guidance cues comprises several members that can function as diffusible axonal chemorepellents. To begin to elucidate the mechanisms that mediate the repulsive actions of Collapsin-1/Semaphorin III/D (Sema III), we searched for Sema III-binding proteins in embryonic rat sensory neurons by expression cloning. We report that Sema III binds with high affinity to the transmembrane protein neuropilin, and that antibodies to neuropilin block the ability of Sema III to repel sensory axons and to induce collapse of their growth cones. These results provide evidence that neuropilin is a receptor or a component of a receptor complex that mediates the effects of Sema III on these axons.

Plexins are a large family of receptors for transmembrane, secreted, and GPI-anchored semaphorins in vertebrates

In Drosophila, plexin A is a functional receptor for semaphorin-1a. Here we show that the human plexin gene family comprises at least nine members in four subfamilies. Plexin-B1 is a receptor for the transmembrane semaphorin Sema4D (CD100), and plexin-C1 is a receptor for the GPI-anchored semaphorin Sema7A (Sema-K1). Secreted (class 3) semaphorins do not bind directly to plexins, but rather plexins associate with neuropilins, coreceptors for these semaphorins. Plexins are widely expressed: in neurons, the expression of a truncated plexin-A1 protein blocks axon repulsion by Sema3A. The cytoplasmic domain of plexins associates with a tyrosine kinase activity. Plexins may also act as ligands mediating repulsion in epithelial cells in vitro. We conclude that plexins are receptors for multiple (and perhaps all) classes of semaphorins, either alone or in combination with neuropilins, and trigger a novel signal transduction pathway controlling cell repulsion.

Ultrapermeable, reverse-selective nanocomposite membranes

Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.

Conversion of neuronal growth cone responses from repulsion to attraction by cyclic nucleotides

Nerve growth is regulated by attractive and repulsive factors in the nervous system. Microscopic gradients of Collapsin-1/Semaphorin III/D (Sema III) and myelin-associated glycoprotein trigger repulsive turning responses by growth cones of cultured Xenopus spinal neurons; the repulsion can be converted to attraction by pharmacological activation of the guanosine 3',5'-monophosphate (cGMP) and adenosine 3',5'-monophosphate signaling pathways, respectively. Sema III also causes the collapse of cultured rat sensory growth cones, which can be inhibited by activation of the cGMP pathway. Thus cyclic nucleotides can regulate growth cone behaviors and may be targets for designing treatments to alleviate the inhibition of nerve regeneration by repulsive factors.

Neuropilin-2, a novel member of the neuropilin family, is a high affinity receptor for the semaphorins Sema E and Sema IV but not Sema III

Semaphorins are a large family of secreted and transmembrane proteins, several of which are implicated in repulsive axon guidance. Neuropilin (neuropilin-1) was recently identified as a receptor for Collapsin-1/Semaphorin III/D (Sema III). We report the identification of a related protein, neuropilin-2, whose mRNA is expressed by developing neurons in a pattern largely, though not completely, nonoverlapping with that of neuropilin-1. Unlike neuropilin-1, which binds with high affinity to the three structurally related semaphorins Sema III, Sema E, and Sema IV, neuropilin-2 shows high affinity binding only to Sema E and Sema IV, not Sema III. These results identify neuropilins as a family of receptors (or components of receptors) for at least one semaphorin subfamily. They also suggest that the specificity of action of different members of this subfamily may be determined by the complement of neuropilins expressed by responsive cells.

Identification of PN1, a predominant voltage-dependent sodium channel expressed principally in peripheral neurons

Membrane excitability in different tissues is due, in large part, to the selective expression of distinct genes encoding the voltage-dependent sodium channel. Although the predominant sodium channels in brain, skeletal muscle, and cardiac muscle have been identified, the major sodium channel types responsible for excitability within the peripheral nervous system have remained elusive. We now describe the deduced primary structure of a sodium channel, peripheral nerve type 1 (PN1), which is expressed at high levels throughout the peripheral nervous system and is targeted to nerve terminals of cultured dorsal root ganglion neurons. Studies using cultured PC12 cells indicate that both expression and targeting of PN1 is induced by treatment of the cells with nerve growth factor. The preferential localization suggests that the PN1 sodium channel plays a specific role in nerve excitability.

RPA involvement in the damage-recognition and incision steps of nucleotide excision repair

Human replication protein (RPA) functions in DNA replication, homologous recombination and nucleotide excision repair. This multisubunit single-stranded DNA-binding protein may be required to make unique protein-protein contacts because heterologous single-stranded binding proteins cannot substitute for RPA in these diverse DNA transactions. We report here that, by using affinity chromatography and immunoprecipitation, we found that human RPA bound specifically and directly to two excision repair proteins, the xeroderma pigmentosum damage-recognition protein XPA (refs 8, 9) and the endonuclease XPG (refs 10-13). Although it had been suggested that RPA might function before the DNA synthesis repair stage, our finding that a complex of RPA and XPA showed a striking cooperativity in binding to DNA lesions indicates that RPA may function at the very earliest stage of excision repair. In addition, by binding XPG, RPA may target this endonuclease to damaged DNA.

Perception of brassinosteroids by the extracellular domain of the receptor kinase BRI1

An assay was developed to study plant receptor kinase activation and signaling mechanisms. The extracellular leucine-rich repeat (LRR) and transmembrane domains of the Arabidopsis receptor kinase BRI1, which is implicated in brassinosteroid signaling, were fused to the serine/threonine kinase domain of XA21, the rice disease resistance receptor. The chimeric receptor initiates plant defense responses in rice cells upon treatment with brassinosteroids. These results, which indicate that the extracellular domain of BRI1 perceives brassinosteroids, suggest a general signaling mechanism for the LRR receptor kinases of plants. This system should allow the discovery of ligands for the LRR kinases, the largest group of plant receptor kinases.

Cellular localization of gene expression for progranulin

Granulins, also called epithelins, are 6-kD peptides with growth modulatory effects on a variety of cells. The granulin/epithelin precursor supports tumorigenesis in appropriate cell models and is the only growth factor able to overcome the cell cycle block that occurs in murine fibroblasts after deletion of a functional IGF-1 receptor. However, little is known of the role of granulin/epithelin gene products in vivo. To understand the physiological role of granulins it is essential to know the cell types and conditions in which it is expressed. We examined granulin/epithelin gene expression in adult rodents by in situ hybridization. The granulin/epithelin precursor is constitutively expressed in a number of epithelia, particularly in the skin, GI tract, and reproductive system. Other epithelia express the gene less strongly. Progranulin is expressed in immune cells in vivo and in specific neurons in the brain, including Purkinje cells, pyramidal cells of the hippocampus, and some cerebral cortical neurons. Little expression was detected in muscle cell, connective tissue, or endothelium. Cumulatively, these results define the basal gene expression of a new growth factor system and suggest that the progranulin/epithelin gene is multifunctional, with important constitutive roles in epithelial homeostasis, reproductive, immunological, and neuronal function.

Semaphorin-neuropilin interactions underlying sympathetic axon responses to class III semaphorins

Neuropilin-1 and neuropilin-2 show specificity in binding to different class III semaphorins, including Sema III, Sema E, and Sema IV, suggesting that the specificity of action of these semaphorins is dictated by the complement of neuropilins expressed by responsive neurons. In support of this, we show that sympathetic axons coexpress neuropilin-1 and -2, that their responses to Sema III, Sema E, and Sema IV are affected in predicted ways by antibodies to neuropilin-1, and that neuropilin-1 and -2 can form homo- and heterooligomers through an interaction involving at least partly the neuropilin MAM (meprin, A5, mu) domain. These results support the idea that in sympathetic axons, the Sema III signal is mediated predominantly by neuropilin-1 oligomers, the Sema IV signal by neuropilin-2 oligomers, and the Sema E signal by neuropilin-1 and -2, either as homo- or heterooligomers.

Surfaces versus features in visual search

Often implicit in the interpretation of visual search tasks is the assumption that the detection of targets is determined by the feature-coding properties of low-level visual processing. But higher level processes have also been implicated as visual search ability is enhanced in a depth plane or when two-dimensional shapes are interpreted as three-dimensional forms. Here we manipulate binocular disparity to degrade visual search, so that otherwise identical features become parts of surfaces through perceptual completion, rendering them less clearly distinguishable as targets and distractors. Our results indicate that visual search has little or no access to the processing level of feature extraction but must have as an input a higher level process of surface representation.

Distance determined by the angular declination below the horizon

A biological system is often more efficient when it takes advantage of the regularities in its environment. Like other terrestrial creatures, our spatial sense relies on the regularities associated with the ground surface. A simple, but important, ecological fact is that the field of view of the ground surface extends upwards from near (feet) to infinity (horizon). It forms the basis of a trigonometric relationship wherein the further an object on the ground is, the higher in the field of view it looks, with an object at infinity being seen at the horizon. Here, we provide support for the hypothesis that the visual system uses the angular declination below the horizon for distance judgement. Using a visually directed action task, we found that when the angular declination was increased by binocularly viewing through base-up prisms, the observer underestimated distance. After adapting to the same prisms, however, the observer overestimated distance on prism removal. Most significantly, we show that the distance overestimation as an after-effect of prism adaptation was due to a lowered perceived eye level, which reduced the object's angular declination below the horizon.

Functional comparison of the three isoforms of the Na+/Ca2+ exchanger (NCX1, NCX2, NCX3)

Three distinct mammalian Na+/Ca2+ exchangers have been cloned: NCX1, NCX2, and NCX3. We have undertaken a detailed functional comparison of these three exchangers. Each exchanger was stably expressed at high levels in the plasma membranes of BHK cells. Na+/Ca2+ exchange activity was assessed using three different complementary techniques: Na+ gradient-dependent 45Ca2+ uptake into intact cells, Na+ gradient-dependent 45Ca2+ uptake into membrane vesicles isolated from the transfected cells, and exchange currents measured using giant patches of excised cell membrane. Apparent affinities for the transported ions Na+ and Ca2+ were markedly similar for the three exchangers at both membrane surfaces. Likewise, generally similar responses to changes in pH, chymotrypsin treatment, and application of various inhibitors were obtained. Depletion of cellular ATP inhibited NCX1 and NCX2 but did not affect the activity of NCX3. Exchange activities of NCX1 and NCX3 were modestly increased by agents that activate protein kinases A and C. All exchangers were regulated by intracellular Ca2+. NCX1-induced exchange currents were especially large in excised patches and, like the native myocardial exchanger, were stimulated by ATP. Results may be influenced by our choice of expression system and specific splice variants, but, overall, the three exchangers appear to have very similar properties.

The transactivator proteins VP16 and GAL4 bind replication factor A

Many transcription factors can activate the initiation of DNA replication. We have used affinity chromatography to show that the acidic activation domains of the transcription factors VP16, GAL4, and p53 each bind selectively to human and yeast replication factor A (RPA). The binding is direct and to the largest subunit of the trimeric RPA complex, RPA-1. Mutations in VP16 that reduce the ability of GAL4-VP16 to activate polyomavirus DNA replication also compromise the binding of VP16 to RPA. We suggest that transcription factors may interact with RPA either to stabilize single-stranded DNA at a replication origin or to recruit DNA polymerase alpha to the replication initiation complex.

Odontogenic tumors. A demographic study of 759 cases in a Chinese population

Seven hundred fifty-nine cases of odontogenic tumors retrieved from the files of College of Stomatology, West China University of Medical Sciences were classified according to the World Health Organization's Histological Classification of Odontogenic Tumors and compared with similar reports from other countries. Among these cases, 93.9% of the tumors were benign and 6.1% were malignant. Ameloblastomas predominated (58.6%) with a predilection for the mandible, while odontomas, generally regarded as the most frequent odontogenic tumor in North America, only accounted for 6.7%, the fourth most common tumor in this series. The mandible and the maxilla were divided into eight anatomic regions, and the distribution of each odontogenic tumor type amongst these regions was recorded. The relative incidence of each tumor type, patient age and gender were also compared with data from other selected large series. Geographic differences were noted in the relative incidence of ameloblastoma, odontoma and malignant odontogenic tumors among the Chinese/African, North American and Turkish/German groups. Ameloblastoma and malignant odontogenic tumors are not considered rare in a Chinese population.

The semaphorin receptor plexin-B1 specifically interacts with active Rac in a ligand-dependent manner

Semaphorin molecules serve as axon guidance signals that regulate the navigation of neuronal growth cones. Semaphorins have also been implicated in other biological processes, including the immune response. Plexins, acting either alone or in complex with neuropilins, have recently been identified as functional semaphorin receptors. However, the mechanisms of signal transduction by plexins remain largely unknown. We have demonstrated a direct interaction between plexin-B1 and activated Rac. Rac specifically interacts with the cytosolic domain of plexin-B1, but not with that of plexin-A3 or -C1. Neither RhoA nor Cdc42 interacts with plexin-B1, indicating that the Rac/plexin-B1 interaction is highly specific. The binding of GTP and the integrity of the Rac effector domain are required for the interaction with plexin-B1. Furthermore, we have identified that a Cdc42/Rac interactive binding (CRIB) motif in the cytosolic domain of plexin-B1 is essential for its interaction with active Rac. We have also observed that the semaphorin CD100, a ligand for plexin-B1, stimulates the interaction between plexin-B1 and active Rac. Our results support a model by which activated Rac plays a role in mediating semaphorin signals, resulting in reorganization of actin cytoskeletal structure.

Regulation of cardiac Na(+)-Ca2+ exchanger by the endogenous XIP region

The cardiac sarcolemmal Na(+)-Ca2+ exchanger is modulated by intrinsic regulatory mechanisms. A large intracellular loop of the exchanger participates in the regulatory responses. We have proposed (Li, Z., D.A. Nicoll, A. Collins, D.W. Hilgemann, A.G. Filoteo, J.T. Penniston, J.N. Weiss, J.M. Tomich, and K.D. Philipson. 1991. J. Biol. Chem. 266:1014-1020) that a segment of the large intracellular loop, the endogenous XIP region, has an autoregulatory role in exchanger function. We now test this hypothesis by mutational analysis of the XIP region. Nine XIP-region mutants were expressed in Xenopus oocytes and all displayed altered regulatory properties. The major alteration was in a regulatory mechanism known as Na(+)-dependent inactivation. This inactivation is manifested as a partial decay in outward Na(+)-Ca2+ exchange current after application of Na+ to the intracellular surface of a giant excised patch. Two mutant phenotypes were observed. In group 1 mutants, inactivation was markedly accelerated; in group 2 mutants, inactivation was completely eliminated. All mutants had normal Na+ affinities. Regulation of the exchanger by nontransported, intracellular Ca2+ was also modified by the XIP-region mutations. Binding of Ca2+ to the intracellular loop activates exchange activity and also decreases Na(+)-dependent inactivation. XIP-region mutants were all still regulated by Ca2+. However, the apparent affinity of the group 1 mutants for regulatory Ca2+ was decreased. The responses of all mutant exchangers to Ca2+ application or removal were markedly accelerated. Na(+)-dependent inactivation and regulation by Ca2+ are interrelated and are not completely independent processes. We conclude that the endogenous XIP region is primarily involved in movement of the exchanger into and out of the Na(+)-induced inactivated state, but that the XIP region is also involved in regulation by Ca2+.

Visual attention to surfaces in three-dimensional space

Although attention plays a significant role in vision, its spatial deployment and spread in the third dimension is not well understood. In visual search experiments we show that we cannot easily focus attention across isodepth loci unless they are part of a well-formed surface with locally coplanar elements. Yet we can easily spread our attention selectively across well-formed surfaces that span an extreme range of stereoscopic depths. In cueing experiments, we show that this spread of attention is, in part, obligatory. Attentional selectivity is reduced when targets and distractors are coplanar with or rest on a common receding stereoscopic plane. We conclude that attention cannot be efficiently allocated to arbitrary depths and extents in space but is linked to and spreads automatically across perceived surfaces.

Terrain influences the accurate judgement of distance

Mathematically, three-dimensional space can be represented differently by the cartesian, polar, and other coordinate systems. However, in physical sciences, the choice of representation system is restricted by the need to simplify a machine's computation while enhancing its efficiency. Does the brain, for the same reasons, 'select' the most cost-efficient way to represent the three-dimensional location of objects? As we frequently interact with objects on the common ground surface, it might be beneficial for the visual system to code an object's location using a ground-surface-based reference frame. More precisely, the brain could use a quasi-two-dimensional coordinate system (x(s), y(s)) with respect to the ground surface (s), rather than a strictly three-dimensional coordinate system (x, y, z), thus reducing coding redundancy and simplifying computations. Here we provide support for this view by studying human psychophysical performance in perceiving absolute distance and in visually directed action tasks. For example, when an object was seen on a continuous, homogeneous texture ground surface, the observer judged the distance to the object accurately. However, when similar surface information was unavailable, for example, when the object was seen across a gap in the ground, or across distinct texture regions, distance judgement was impaired.

Binocular rivalry and visual awareness: the role of attention

When the right eye and the left eye view dissimilar scenes, the observer does not experience a stable superimposed percept of the images presented to the two eyes, but instead perceives an alternation between the images seen by each eye. A critical question confronting this robust and intriguing phenomenon of binocular rivalry is how the visual system selects the image to be perceived (dominant). The current main-stream literature emphasizes a bottom-up explanation in which the rivalry stimulus with the higher contour strength has the advantage, and becomes dominant in rivalry. Nevertheless, some workers in the past have favored an attention-selection explanation for binocular rivalry. We investigated the role of attention in binocular rivalry by employing novel psychophysical paradigms which capitalized on several established phenomena (e.g. the Cheshire Cat effect, attention cueing, pop-out effect). Our results revealed two major aspects of attention modulation in binocular rivalry. We found that a dominant image is less likely to be suppressed when voluntary attention is directed to it. This suggests the role of voluntary attention in retaining the dominant image in visual awareness. Second, a rivalry stimulus is more likely to become dominant if accompanied by a pop-out cue (in the same eye and proximity). Since a pop-out cue attracts involuntary attention to its location/eye, this result suggests that cue-mediated involuntary attention can promote the ability of a rivalry stimulus to reach visual awareness.

Semaphorins III and IV repel hippocampal axons via two distinct receptors

The semaphorins are the largest family of repulsive axon guidance molecules. Secreted semaphorins bind neuropilin receptors and repel sensory, sympathetic and motor axons. Here we show that CA1, CA3 and dentate gyrus axons from E15-E17 mouse embryo explants are selectively repelled by entorhinal cortex and neocortex. The secreted semaphorins Sema III and Sema IV and their receptors Neuropilin-1 and −2 are expressed in the hippocampal formation during appropriate stages. Sema III and Sema IV strongly repel CA1, CA3 and dentate gyrus axons; entorhinal axons are only repelled by Sema III. An antibody against Neuropilin-1 blocks the repulsive action of Sema III and the entorhinal cortex, but has no effect on Sema IV-induced repulsion. Thus, chemorepulsion plays a role in axon guidance in the hippocampus, secreted semaphorins are likely to be responsible for this action, and the same axons can be repelled by two distinct semaphorins via two different receptors.

Semaphorins as mediators of neuronal apoptosis

Shrinkage and collapse of the neuritic network are often observed during the process of neuronal apoptosis. However, the molecular and biochemical basis for the axonal damage associated with neuronal cell death is still unclear. We present evidence for the involvement of axon guidance molecules with repulsive cues in neuronal cell death. Using the differential display approach, an up-regulation of collapsin response mediator protein was detected in sympathetic neurons undergoing dopamine-induced apoptosis. A synchronized induction of mRNA of the secreted collapsin-1 and the intracellular collapsin response mediator protein that preceded commitment of neurons to apoptosis was detected. Antibodies directed against a conserved collapsin-derived peptide provided marked and prolonged protection of several neuronal cell types from dopamine-induced apoptosis. Moreover, neuronal apoptosis was inhibited by antibodies against neuropilin-1, a putative component of the semaphorin III/collapsin-1 receptor. Induction of neuronal apoptosis was also caused by exposure of neurons to semaphorin III-alkaline phosphatase secreted from 293EBNA cells. Anti-collapsin-1 antibodies were effective in blocking the semaphorin III-induced death process. We therefore suggest that, before their death, apoptosis-destined neurons may produce and secrete destructive axon guidance molecules that can affect their neighboring cells and thus transfer a "death signal" across specific and susceptible neuronal populations.

Role of protein-protein interactions in the function of replication protein A (RPA): RPA modulates the activity of DNA polymerase alpha by multiple mechanisms

Replication Protein A (RPA) from human cells is a stable complex of 70-, 32-, and 14-kDa subunits that is required for multiple processes in DNA metabolism. RPA binds with high affinity to single-stranded DNA and interacts with multiple proteins, including proteins required for the initiation of SV40 DNA replication, DNA polymerase alpha and SV40 large T antigen. We have used a series of mutant derivatives of RPA to map the regions of RPA required for specific protein-protein interactions and have examined the roles of these interactions in DNA replication. T antigen, DNA polymerase alpha and the activation domain of VP16 all have overlapping sites of interaction in the N-terminal half (residues 1-327) of the 70-kDa subunit of RPA. In addition, the interaction site for DNA polymerase alpha is composed of two functionally distinct regions, one (residues 1- approximately 170) which stimulates polymerase activity and a second (residues approximately 170-327) which increases polymerase processivity. In the latter, both the direct protein-protein interaction and ssDNA-binding activities of RPA were needed for RPA to modulate polymerase processivity. We also found that SV40 T antigen inhibited the ability of RPA to increase processivity of DNA polymerase alpha, suggesting that this activity of RPA may be important for elongation but not during the initiation of DNA replication. DNA polymerase alpha, but not T antigen also interacted with the 32- and/or 14-kDa subunits of RPA, but these interactions did not seem to effect polymerase activity.

Surface strains in the anterior leaflet of the functioning mitral valve

Abstract-The mitral valve (MV) is a complex anatomical structure whose function involves a delicate force balance and synchronized function of each of its components. Elucidation of the role of each component and their interactions is critical to improving our understanding of MV function, and to form the basis for rational surgical repair. In the present study, we present the first known detailed study of the surface strains in the anterior leaflet in the functioning MV. The three-dimensional spatial positions of markers placed in the central region of the MV anterior leaflet in a left ventricle-simulating flow loop over the cardiac cycle were determined. The resulting two-dimensional in-surface strain tensor was computed from the marker positions using a C0 Lagrangian quadratic finite element. Results demonstrated that during valve closure the anterior leaflet experienced large, anisotropic strains with peak stretch rates of 500%-1,000%/s. This rapid stretching was followed by a plateau phase characterized by relatively constant strain state. We hypothesized that the presence of this plateau phase was a result of full straightening of the leaflet collagen fibers upon valve closure. This hypothesis suggests that the MV collagen fibers are designed to allow leaflet coaptation followed by a dramatic increase in stiffness to prevent further leaflet deformation, which would lead to valvular regurgitation. These studies represent a first step in improving our understanding of normal MV function and to help establish the principles for repair and replacement.

The human cytomegalovirus UL97 protein is a protein kinase that autophosphorylates on serines and threonines

The product of the human cytomegalovirus (CMV) UL97 gene, which controls ganciclovir phosphorylation in virus-infected cells, is homologous to known protein kinases but diverges from them at a number of positions that are functionally important. To investigate UL97, we raised an antibody against it and overexpressed it in baculovirus-infected insect cells. Recombinant baculovirus expressing full-length UL97 directed the phosphorylation of ganciclovir in insect cells, which was abolished by a four-codon deletion that confers ganciclovir resistance to CMV. When incubated with [gamma-32P]ATP, full-length UL97 was phosphorylated on serine and threonine residues. Phosphorylation was severely impaired by a point mutation that alters lysine-355 in a motif that aligns with subdomain II of protein kinases. However, phosphorylation was impaired much less severely by the four-codon deletion. A UL97 fusion protein expressed from recombinant baculovirus was purified to near homogeneity. It too was phosphorylated upon incubation with [gamma-32P]ATP in vitro. This phosphorylation, which was abolished by the lysine 355 mutation, was optimal at high NaCl and high pH. The activity required either Mn2+ or Mg2+, with a preference for Mn2+, and utilized either ATP or GTP as a phosphate donor, with Kms of 2 and 4 microM, respectively. The phosphorylation rate was first order with protein concentration, consistent with autophosphorylation. These data strongly argue that UL97 is a serine/threonine protein kinase that autophosphorylates and suggest that the four-codon deletion affects its substrate specificity.