The herpes simplex virus 1 RNA binding protein US11 is a virion component and associates with ribosomal 60S subunits.

The herpes simplex virus 1 US11 gene encodes a site- and conformation-specific RNA binding regulatory protein. We fused the coding sequence of this protein with that of beta-galactosidase, expressed the chimeric gene in Escherichia coli, and purified a fusion protein which binds RNA in the same way as the infected cell protein. The fusion protein was used to generate anti-US11 monoclonal antibody. Studies with this antibody showed that US11 protein is a viral structural protein estimated to be present in 600 to 1,000 copies per virion. The great majority of cytoplasmic US11 protein was found in association with the 60S subunit of infected cell ribosomes. US11 protein associates with ribosomes both late in infection at the time of its synthesis and at the time of infection after its introduction into the cytoplasm by the virion. US11 protein expressed in an uninfected cell line stably transfected with the US11 gene associates with ribosomal 60S subunits and localizes to nucleoli, suggesting that US11 protein requires no other viral functions for these associations.     

RNA-protein interactions of stored 5S RNA with TFIIIA and ribosomal protein L5 during Xenopus oogenesis

We studied the pathway of 5S RNA during oogenesis in Xenopus laevis from its storage in the cytoplasm to accumulation in the nucleus, the sequence requirements for the 5S RNA to follow that pathway, and the 5S RNA-protein interactions that occur during the mobilization of stored 5S RNA for assembly into ribosomes. In situ hybridization to sections of oocytes indicates that 5S RNA first becomes associated with the amplified nucleoli during vitellogenesis when the nucleoli are activity synthesizing ribosomal RNA and assembling ribosomes. When labeled 5S RNA is microinjected into the cytoplasm of stage V oocytes, it migrates into the nucleus, whether microinjected naked or complexed with the protein TFIIIA as a 7S RNP storage particle. During vitellogenesis, a nonribosome bound pool of 5S RNA complexed with ribosomal protein L5 (5S RNPs) is formed, which is present throughout the remainder of oogenesis. Immunoprecipitation assays on homogenates of microinjected oocytes showed that labeled 5S RNA can become complexed either with L5 or with TFIIIA. Nucleotides 11 through 108 of the 5S RNA molecule provide the necessary sequence and conformational information required for the formation of immunologically detectable complexes with TFIIIA or L5 and for nuclear accumulation. Furthermore, labeled 5S RNA from microinjected 7S RNPs can subsequently become associated with L5. Such labeled 5S RNA is found in both 5S RNPs and 7S RNPs in the cytoplasm, but only in 5S RNPs in the nucleus of microinjected oocytes. These data suggest that during oogenesis a major pathway for incorporation of 5S RNA into nascent ribosomes involves the migration of 5S RNA from the nucleus to the cytoplasm for storage in an RNP complex with TFIIIA, exchange of that protein association for binding with ribosomal protein L5, and a return to the nucleus for incorporation into ribosomes as they are being assembled in the amplified nucleoli.     

In situ hybridization and immuno-electron microscope analyses of the Us11 gene of herpes simplex virus type 1 during transient expression

The distribution of Us11 RNA and of its encoded protein have been investigated at the ultrastructural level in HeLa cells transiently expressing the Us11 gene of herpes simplex virus type 1. In these transfected cells, Us11 protein accumulates at sites identical to those of lytically infected cells, i.e., in nucleoli and in regions of the cytoplasm that contain ribosomes. Us11 RNA and polyadenylated RNA are scattered over the ribosomerich areas of the cytoplasm. They also accumulate in the nucleoplasm on clustered ribonucleoprotein (RNP) fibrils but also in clusters of interchromatin granules, some of them contiguous to nucleoli. However they are never found in nucleoli. These data reveal the involvement of interchromatin granules in some steps of Us11 mRNA maturation and/or transport.     

Nuclear entry and nucleolar localization of the Newcastle disease virus (NDV) matrix protein occur early in infection and do not require other NDV proteins.

A large proportion of the Newcastle disease virus (NDV) matrix (M) protein is found in the nuclei of infected chicken embryo cells. Kinetic analysis indicated that much of the M protein enters the nucleus early in infection, concentrating in discrete regions of the nucleus and remaining there throughout infection. The M protein was found in localized regions of the nuclei of a variety of cell lines infected with NDV. Immunostaining for both M protein and nucleolar antigens indicated that most of these regions represent nucleoli. Moreover, this nucleolar localization of the M protein was observed in chicken embryo cells infected with 11 different strains of NDV. Only the M protein of strain HP displayed a modified pattern, concentrating in the nucleolus early in infection but in the cytoplasm late in infection. M protein transiently expressed in COS-1 cells also localized to the nucleus and nucleolus, indicating that the M protein does not require other NDV proteins for this localization.     

Some chemical properties of isolated pea nucleoli

Isolated nuclei and nucleoli of ungerminated pea embryos have been analyzed chemically for their content of DNA, RNA, zinc, iron, phosphorus, and protein sulfhydryl groups. The values obtained cannot be considered to represent the whole of the living nucleolar body as an undetermined amount of material is extracted from nucleoli in the course of their isolation. Only negligible amounts of DNA have been found in the isolated nucleoli; most of the DNA released on disruption of nuclei appears in a fraction showing very few structures under the light microscope. RNA is more concentrated in the nucleolus than in the nucleus or cytoplasm, but since nucleolar protein is 6 per cent of nuclear and less than 1 per cent of cytoplasmic protein, the total amount of nucleolar RNA is comparatively small. None of the other components listed occurs in high concentration in either nucleus or nucleolus.     

Some Chemical Properties of Isolated Pea Nucleoli

Isolated nuclei and nucleoli of ungerminated pea embryos have been analyzed chemically for their content of DNA, RNA, zinc, iron, phosphorus, and protein sulfhydryl groups. The values obtained cannot be considered to represent the whole of the living nucleolar body as an undetermined amount of material is extracted from nucleoli in the course of their isolation. Only negligible amounts of DNA have been found in the isolated nucleoli; most of the DNA released on disruption of nuclei appears in a fraction showing very few structures under the light microscope. RNA is more concentrated in the nucleolus than in the nucleus or cytoplasm, but since nucleolar protein is 6 per cent of nuclear and less than 1 per cent of cytoplasmic protein, the total amount of nucleolar RNA is comparatively small. None of the other components listed occurs in high concentration in either nucleus or nucleolus.     

Simian Virus 40-Host Cell Interactions II. Cytoplasmic and Nucleolar Accumulation of Simian Virus 40 Virion Protein

We have used immunofluorescence in parallel with transmission and scanning electron microscopy to characterize the unusual cytoplasmic and nucleolar accumulation of Simian virus 40 (SV40) virion protein (C antigen) at restrictive temperatures (39 to 41 C) in monkey cells infected with a temperature-sensitive mutant of SV40 defective in virion assembly, tsB11. Cytoplasmic and nucleolar accumulation of C antigen did not occur in wild-type-infected cells at any temperature. Wild-type- and tsBll-infected cells were not distinguishable at 33 C by immunofluorescence or electron microscopy. Temperature-shift experiments using metabolic inhibitors of DNA (cytosine arabinonucleoside, 20 mug/ml), RNA (actinomycin D, 5 mug/ml), and protein synthesis (cycloheximide, 2 x 10(-4) to 10 x 10(-4) M) were used to investigate the requirements for ongoing DNA, RNA, and protein synthesis in the distribution of virion protein between the nucleus, nucleolus, and cytoplasm. The transport of C antigen from the nucleolus and cytoplasm into the nucleus was complete after a temperature shift-down (41 and 39 to 33 C). Limited virus particle formation occurred after the shift-down in the presence of actinomycin D and cycloheximide, indicating some of the 39 to 41 C synthesized virion protein could be used for capsid assembly at 33 C in the absence of further virion protein synthesis. Nucleolar and cytoplasmic accumulations of C antigen occurred in the absence of drugs after a shift-up (33 to 39 C and 41 C) indicating a continuous requirement for the tsB11 mutant function. Furthermore, the virion protein synthesized at 33 C remained confined to the nucleus when the cells were shifted to 39 and 41 C in the presence of actinomycin D or cycloheximide. In the presence of cytosine arabinonucleoside, however, the virion protein accumulated in large aggregates in the nucleus and nucleolus after the shift-up, but did not migrate into the cytoplasm as it did in drug-free tsB11-infected control cells. Colchicine (10(-3) M) had no effect on the abnormal accumulation of C antigen during shift-up or shift-down experiments suggesting that microtubular transport plays little if any role in the abnormal transport of tsB11 virion protein from cytoplasm to nucleus. Although virus particles were never observed by electron microscopy and V antigen was not detected by immunofluorescence at 39 or 41 C in tsB11-infected cells, dense amorphous accumulations were formed in the nucleoli and cytoplasm. We suggest that the tsB11 function is continuously required for the normal transport of SV40 virion protein between the cytoplasm, nucleolus, and nucleus and for the assembly of capsids and virions. Several possible mechanisms for the altered tsB11 function or protein are discussed. One of the virion proteins may also be involved in some presently undetermined nucleolar function during SV40 productive infection.     

Dynamic distribution of the regulatory subunit of cAMP-dependent protein kinase type II in NIH 3T3 cells

Experiments on the introduction of the regulatory subunit of cAMP-dependent protein kinase type II (RII) into NIH 3T3 cells clearly demonstrated its translocation into the nucleus. The labelled protein was incorporated into erythrocyte ghosts and their fusion with the cells was carried out. The dynamics of distribution of the labelled RII in NIH 3T3 cells was studied by the method of historadiography. It was found that during the next few hours after its penetration into the cytoplasm, the protein translocates into the nucleus and concentrates in the immediate proximity to the nucleoli.     

The herpes simplex virus 1 UL11 proteins are associated with cytoplasmic and nuclear membranes and with nuclear bodies of infected cells.

Earlier studies have shown that the UL11 gene of herpes simplex virus encodes a myristylated virion protein and that the UL11 gene enables efficient virion envelopment and export from infected cells. A rabbit polyclonal antibody directed against an affinity-purified UL11-glutathione-S-transferase fusion protein was made and used to study the properties of the UL11 protein and its distribution in infected cells. We report the following: (i) UL11 protein formed up to five bands (apparent M(r)s, 17,000 to 22,000) in denaturing polyacrylamide gels; (ii) fluorescent-antibody studies revealed the presence of UL11 protein in the perinuclear space and in sites within the nucleus; (iii) immune electron microscopic studies indicated that the UL11 gene products were associated with the inner nuclear membrane, with cytoplasmic membranes and ribbon-like cytoplasmic structures resembling membranous organelles, with nuclear bodies shown by fluorescence microscopy to be different from nucleoli in which US11 protein accumulates, and with enveloped virions but not with nuclear capsids; and (iv) the nuclear bodies containing UL11 protein were reminiscent both of type IV morphotypes consisting of an electron-dense core containing the UL11 proteins surrounded by a more electron-transluscent core and of type V morphotypes consisting of material homogenous in electron opacity. We conclude that (i) the UL11 protein is processed after synthesis; (ii) the localization of UL11 protein with virions and membranes is consistent with the hypothesis that UL11 plays a role in the transport of virions to the extracellular space; and (iii) although the significance of the association of UL11 proteins with nuclear bodies is unknown, the results indicate that nuclear bodies differ with respect to their morphologies and contents of viral protein and suggest that UL11 protein may have more than one function in the infected cell.     

Intracellular Amounts of Nucleic Acids and Protein During Pollen Grain Growth in Tradescantia

The rapid growth, large organelles, and synchronous development of T. paludosa pollen grains make them ideal subjects for cytochemical analysis. A microphotometric study of the nucleoli, chromosomes, and cytoplasm fixed at daily intervals during pollen grain maturation indicated that: 1. DNA (Feulgen) synthesis in the generative nucleus occurred during the first third of interphase, while the DNA content of the vegetative nucleus remained unchanged. 2. Throughout development, changes in RNA (azure B) content, in general, paralleled changes in protein (NYS¹, Millon) content in each organelle of the vegetative cell. Initially, the RNA and protein of all organelles increased up to mid interphase, when chromosomal and nucleolar fractions began to decline despite a continued increase in cytoplasmic RNA and protein. At least 24 hours before anthesis, the vegetative nucleolus had disappeared and chromosomal protein and RNA of the vegetative nucleus were apparently in rapid decline. Such a system offered an opportunity to study the role of the nucleus, especially the nucleolus, in RNA and protein metabolism in the cytoplasm, by noting what cytoplasmic processes could and could not continue at a time when nuclear mechanisms were absent or minimal. It was found that at least 2 fundamental processes continued during this period: both RNA and protein accumulated in the cytoplasm at a rapid rate. It was concluded that the nucleus is not the sole source of cytoplasmic RNA, for the data suggest that there are at least 2 separate and independent, or remotely dependent synthesizing systems, one nuclear and the other cytoplasmic. It is evident that nuclear influence on cytoplasmic synthesis need be neither direct nor immediate.     

Structure and function in the herpes simplex virus 1 RNA-binding protein U(s)11: mapping of the domain required for ribosomal and nucleolar association and RNA binding in vitro.

The herpes simplex virus 1 US11 protein is an RNA-binding regulatory protein that specifically and stably associates with 60S ribosomal subunits and nucleoli and is incorporated into virions. We report that US11/ beta-galactosidase fusion protein expressed in bacteria bound to rRNA from the 60S subunit and not the 40S subunit. This binding reflects the specificity of ribosomal subunit association. Analyses of deletion mutants of the US11 gene showed that specific RNA binding activity, nucleolar localization, and association with 60S ribosomal subunits were found to map to the amino acid sequences of the carboxyl terminus of US11 protein, suggesting that these activities all reflect specific binding of US11 to large subunit rRNA. The carboxyl-terminal half of the protein consists of a regular tripeptide repeat of the sequence RXP and constitutes a completely novel RNA-binding domain. All of the mutant US11 proteins could be incorporated into virus particles, suggesting that the signal for virion incorporation either is at the amino-terminal four amino acids or is redundant in the protein.     

Subcellular localization of the 84,000 dalton heat-shock protein in mouse neuroblastoma cells: evidence for a cytoplasmic and nuclear location

Using affinity-purified antibodies, the 84,000 dalton heat-shock protein (hsp) has been localized in mouse N2A neuroblastoma cells by immunocytochemical techniques. Immunofluorescence microscopy showed that hsp84 was present both in the cytoplasm and in the nucleus. The nucleoli were found to be unlabelled. Immunogold labelling on ultrathin cryosections revealed that hsp84 was evenly distributed throughout the entire cytoplasm. No preferential association of hsp84 with the plasma membrane or with membranes from organelles was observed. In the nucleus the hsp84 was present in both the euchromatin and heterochromatin. In the nucleolus only the fibrillar part was labelled and virtually no gold particles were observed in the granular part. A long-term hyperthermic treatment of 3 h at 42.5 degrees C was found to induce an accumulation of hsp84 inside the nucleus. No alterations in hsp84 distribution were observed during a treatment of the cells with 75 microM sodium arsenite for 3 h. Drastic alterations were observed in the nucleoli after both stress treatments. The granular part had totally disappeared and only remnants of the fibrillar part which contained hsp84, were found. Besides the nuclear accumulations of hsp84 during heat shock, no additional changes in the hsp84 location in stressed cells were observed. During a recovery from the heat shock by replacing the cells at 37 degrees C, a decrease in the nuclear location of hsp84 was observed, indicating the reversibility of this process. The significance of these results for the role of hsp84 in normal and in stressed cells is discussed.     

Poroid hidradenoma. Report of a case with cytologic findings on fine needle aspiration.

BACKGROUND: Fine needle aspiration cytology (FNAC) can be used for establishing a diagnosis of cutaneous lesions, especially in cases with cyst formation. Poroid hidradenoma is eccrine neoplasm with both solid and cystic components. CASE: A 77-year-old female presented with a slightly elevated nodule in the skin on her left elbow. The tumor was well demarcated, 2.7 x 2.4 cm and soft, and overlying skin was slightly reddish. FNAC revealed two types of cell: one had abundant cytoplasm in which small to large, occasionally multinucleated nuclei with small but distinct nucleoli were evident. Chromatin was finely granular, and nuclear membrane was thin and almost smooth. Another type of cell had scanty cytoplasm and a round to oval nucleus with small but prominent nucleoli. Histologic diagnosis was poroid hidradenoma. CONCLUSION: FNAC can be useful for diagnosing intradermal cystic lesions before surgical resection.     

Functional anatomy of herpes simplex virus 1 overlapping genes encoding infected-cell protein 22 and US1.5 protein

Earlier studies have shown that (i) the coding domain of the alpha22 gene encodes two proteins, the 420-amino-acid infected-cell protein 22 (ICP22) and a protein, US1.5, which is initiated from methionine 147 of ICP22 and which is colinear with the remaining portion of that protein; (ii) posttranslational processing of ICP22 mediated largely by the viral protein kinase UL13 yields several isoforms differing in electrophoretic mobility; and (iii) mutants lacking the carboxyl-terminal half of the ICP22 and therefore DeltaUS1.5 are avirulent and fail to express normal levels of subsets of both alpha (e.g., ICP0) or gamma2 (e.g., US11 and UL38) proteins. We have generated and analyzed two sets of recombinant viruses. The first lacked portions of or all of the sequences expressed solely by ICP22. The second set lacked 10 to 40 3'-terminal codons of ICP22 and US1. 5. The results were as follows. (i) In cells infected with mutants lacking amino-terminal sequences, translation initiation begins at methionine 147. The resulting protein cannot be differentiated in mobility from authentic US1.5, and its posttranslational processing is mediated by the UL13 protein kinase. (ii) Expression of US11 and UL38 genes by mutants carrying only the US1.5 gene is similar to that of wild-type parent virus. (iii) Mutants which express only US1. 5 protein are avirulent in mice. (iv) The coding sequences Met147 to Met171 are essential for posttranslational processing of the US1.5 protein. (v) ICP22 made by mutants lacking 15 or fewer of the 3'-terminal codons are posttranslationally processed whereas those lacking 18 or more codons are not processed. (vi) Wild-type and mutant ICP22 proteins localized in both nucleus and cytoplasm irrespective of posttranslational processing. We conclude that ICP22 encodes two sets of functions, one in the amino terminus unique to ICP22 and one shared by ICP22 and US1.5. These functions are required for viral replication in experimental animals. US1.5 protein must be posttranslationally modified by the UL13 protein kinase to enable expression of a subset of late genes exemplified by UL38 and US11. Posttranslational processing is determined by two sets of sequences, at the amino terminus and at the carboxyl terminus of US1.5, respectively, a finding consistent with the hypothesis that both domains interact with protein partners for specific functions.     

Bertalanffy-like fluorescence staining with 3-dimethylamino-6-methoxyacridine

Three new acridine dyes, 3-dimethylamino-6-methoxyacridine 1, 3-amino-6-methoxyacridine 2 and 3-amino-7-methoxyacridine 3, have been prepared and tested as fluorochromes of LM- and HeLa-cells. The dyes are basic compounds (pKA: 1 8,76; 2 8,01; 3 7,65) and form cations in neutral or acidic aqueous solutions by addition of a proton to the aza-nitrogen atom of the heterocycle. The fluorochromes stain fixed LM- and HeLa-cells at pH = 6. The fluorescence shows metachromasy similar to the staining with acridine orange AO according to the technique of Bertalanffy. But there is less fading of the fluorescence. The dye 1 is the most suitable fluorochrome of the series. It was studied in detail. Using optimized staining conditions the fluorescence of the nucleus is yellow-green that of the cytoplasm and the nucleoli orange or brownish-red. Enzymatic digestion experiments show that the dye cations are bound to DNA in the nucleus and to RNA in the cytoplasm or nucleoli. The absorption and emission spectra of the stained cells have been studied by means of microspectrophotometry. The absorption spectra of the nucleus and the cytoplasm are very similar. The maximum of the long wave length absorption of both occurs at 21400 cm-1 (467 nm) with a shoulder at ca 20100 cm-1 (498 nm). The fluorescence spectra of nucleus and cytoplasm of metachromatically stained cells are different. The emission maximum of the cytoplasm and nucleoli, 16200 cm-1 (617 nm), is red-shifted relative to the maximum of the nucleus, 18200 cm-1 (549 nm). This shift causes the metachromatic fluorescence effect. In addition we studied the concentration dependence of the absorption and fluorescence spectra of the cation 1 in aqueous solution, pH = 6, in the concentration range 6 X 10(-6)-6 X 10(-4) M. Shape and maximum of the long wave length absorption and emission depend only slightly on the concentration: Mean value of absorption maximum ca 21500 cm-1 (465 nm), shoulder at ca 20300 cm-1 (493 nm), fluorescence maximum ca 18300 cm-1 (547 nm). With growing concentration diminishes the molar absorptivity. This decrease in absorptivity and isosbestic points in the absorption spectra indicate the formation of dimers with growing dye concentration. The absorption spectra of the metachromatically stained cells and of the dye in aqueous solution are very similar.(ABSTRACT TRUNCATED AT 400 WORDS)     

Nuclear functions of the Arf guanine nucleotide exchange factor BRAG2

BRAG2 is a guanine nucleotide exchange factor for the GTPase Arf6 that cycles between the cytoplasm and nucleus in a CRM1/exportin1-dependent manner. Despite its presence in the nucleus, nuclear functions have not previously been described. Here, we show that depletion of endogenous BRAG2 by RNAi leads to an increased number of Cajal bodies (CBs), and altered structure of nucleoli, as indicated by less focal fibrillarin staining. This result was surprising given that nuclear BRAG2 is diffusely distributed throughout the nucleoplasm and is not concentrated within nucleoli at steady state. However, we found that ectopic expression of the nuclear GTPase PIKE/AGAP2 causes both BRAG2 and the CB marker coilin to accumulate in nucleoli. Neither the GTPase activity of PIKE nor the nucleotide exchange activity of BRAG2 is required for this nucleolar concentration. Increased levels of exogenous BRAG2 in nucleoli result in a redistribution of fibrillarin to the nucleolar periphery, supporting a role for BRAG2 in regulating nucleolar architecture. These observations suggest that, in addition to its role in endocytic regulation at the plasma membrane, BRAG2 also functions within the nucleus.     

Plant nuclei can contain extensive grooves and invaginations

Plant cells can exhibit highly complex nuclear organization. Through dye-labeling experiments in untransformed onion epidermal and tobacco culture cells and through the expression of green fluorescent protein targeted to either the nucleus or the lumen of the endoplasmic reticulum/nuclear envelope in these cells, we have visualized deep grooves and invaginations into the large nuclei of these cells. In onion, these structures, which are similar to invaginations seen in some animal cells, form tubular or planelike infoldings of the nuclear envelope. Both grooves and invaginations are stable structures, and both have cytoplasmic cores containing actin bundles that can support cytoplasmic streaming. In dividing tobacco cells, invaginations seem to form during cell division, possibly from strands of the endoplasmic reticulum trapped in the reforming nucleus. The substantial increase in nuclear surface area resulting from these grooves and invaginations, their apparent preference for association with nucleoli, and the presence in them of actin bundles that support vesicle motility suggest that the structures might function both in mRNA export from the nucleus and in protein import from the cytoplasm to the nucleus.     

Nuclear export of human immunodeficiency virus type 1 Vpr is not required for virion packaging

The human immunodeficiency virus type 1 Vpr protein is both packaged into virions and efficiently localized to the nucleus. In this report, we show that a significant fraction of Vpr also accumulates in the cytoplasm of virus-producing cells. Although Vpr shuttles between the nucleus and the cytoplasm, studies with an export-deficient Vpr mutant reveal that nuclear export is not required for virion incorporation.     

Karyophilic properties of Semliki Forest virus nucleocapsid protein.

Semliki Forest virus capsid (C) protein molecules (Mr, 33,000) can be introduced efficiently into the cytoplasm of various target cells by electroporation, liposome, and erythrocyte ghost-mediated delivery (M. Elgizoli, Y. Dai, C. Kempf, H. Koblet, and M.R. Michel, J. Virol. 63:2921-2928, 1989). Here, we show that the transferred C protein molecules partition rapidly from the cytosolic compartment into the nucleus. Transport of the C protein molecules into the nucleus was reversibly arrested by metabolic inhibitors, indicating that the transfer process is energy dependent. Fractionation of isolated nuclei revealed that the delivered C protein preferentially associates with the nucleoli. This finding was confirmed by morphological studies, showing that in an in vitro system containing ATP isolated nuclei rapidly accumulated rhodamine-labeled C protein in their nucleoli. Furthermore, in this assay system, the lectin wheat germ agglutinin prevented transfer of C protein through nuclear pores. These results are in agreement with our observation that nucleoli contain measurable amounts of newly synthesized C protein as early as 5 h after infection of cells with SFV. Thereafter, nucleolar-associated C protein increased progressively during the course of infection.     

Nucleolin is required for an efficient herpes simplex virus type 1 infection

Productive infection by herpes simplex virus type 1 (HSV-1), which occurs in the host cell nucleus, is accompanied by dramatic modifications of the nuclear architecture, including profound alterations of nucleolar morphology. Here, we show that the three most abundant nucleolar proteins--nucleolin, B23, and fibrillarin--are redistributed out of the nucleoli as a consequence of HSV-1 infection. We show that the amount of nucleolin increases progressively during the course of infection. We demonstrate for the first time that a nucleolar protein, i.e., nucleolin, colocalizes with ICP8 in the viral replication compartments, at the time when viral replication is effective, suggesting an involvement of nucleolin in the HSV-1 DNA replication process. At later times of infection, a granular form of nucleolin localizes to the cytoplasm, in structures that display the characteristic features of aggresomes, indicating that this form of nucleolin is very probably destined for degradation. The delocalization of nucleolin from the nucleoli requires the viral ICP4 protein or a factor(s) whose expression involves ICP4. Using small interfering RNA technology, we show that viral replication requires a high level of nucleolin expression, demonstrating for the first time a direct role for a nucleolar protein in herpes simplex virus biology.