Growth characteristics of cytomegalovirus in human fibroblasts with demonstration of protein synthesis early in viral replication

Effect of DNA polymerase inhibitors on the replication of human cytomegalovirus. Brief report

Aphidicolin, a specific inhibitor of cellular DNA polymerase alpha and of viral DNA polymerase, inhibits production of infectious virus and cellular and viral DNA synthesis of human cytomegalovirus (HCMV)-infected cells. On the other hand, 2',3'-dideoxynucleosides, inhibitors of DNA polymerases beta and gamma, do not affect HCMV replication. The data show that the alpha DNA polymerases of either viral or cellular origin are required for viral DNA synthesis, and cannot be substituted by the cellular DNA polymerase beta and gamma.

Glycosphingolipid synthesis in human fibroblasts infected by cytomegalovirus

Infection of serum-deprived human foreskin fibroblasts (HFF-cells) by cytomegalovirus (HCMV) resulted in enhanced precursor incorporation into glycosphingolipids (GSL). Analysis of the component patterns revealed a unique biphasic effect on the rate labeling of neutral GSL. Early during infection or in the presence of phosphonoacetic acid, radiolabel was found predominantly in ceramide tri- and tetrahexoside, whereas late after infection label in ceramide monohexoside exceeded that in the other components. Determination of the chemical amounts of neutral GSL components from infected cultures supported the view of increased biosynthesis of ceramide tri- and tetrahexoside early, and of ceramide monohexoside late postinfection. Changes, comparable to those observed under the influence of "early" viral functions were observed also during S-phase of serum-stimulated HFF cells. With respect to acidic GSL a decrease of metabolic labeling occurred late during infection. Relatively little alteration was found in the component pattern.

A variant of human cytomegalovirus derived from a persistently infected culture

Infection of cells derived from an osteogenic sarcoma (HOS) with human cytomegalovirus (HCMV) resulted in persistent infection. It appears that persistent infection is due to a balance between release of virus and the growth of uninfected cells. Viruses derived from the persistently infected cultures were not temperature sensitive nor were they defective interfering particles. However, hybridization experiments using the Q-labeled probe from the XbaI Q fragment indicated that one copy of the repeat sequences contained in fragments Q and O of CMV, Towne DNA have been completely deleted from the virus DNA derived from the persistent culture. Thus the mechanism of persistent infection is probably due in part to a variant of CMV present in the cultures.

Properties of a human cytomegalovirus-induced protein kinase

A human cytomegalovirus (HCMV)-induced polypeptide of 68,000 Da (p68) with protein kinase activity was identified using a monoclonal antibody (F6b) produced against HCMV-infected cell proteins. p68 was detected by immunoprecipitation from 3 to 120 hr after infection and was induced by several strains of human and not simian CMV. Protein kinase activity was associated almost exclusively with nuclear HCMV-induced p68. Enzyme activity with ATP and casein as phosphate donor and acceptor, respectively, exhibited an optimum pH between 6 and 6.5. It was Mg2+ dependent and cAMP independent. The KATPm of 45 microM at pH 6.5 indicated a relatively high affinity of p68 for the nucleotide. p68 also transferred phosphate to phosvitin and light chains of F6b, as well as autophosphorylating at threonine and serine residues.

Cytomegalovirus replicates in differentiated but not in undifferentiated human embryonal carcinoma cells

To study the mode of action of human cytomegalovirus, an important teratogenic agent in human populations, the susceptibility of a pluripotent human embryonal carcinoma cell line to the virus was investigated. Viral antigens were not expressed nor was infectious virus produced by human embryonal carcinoma cells after infection, although the virus was able to penetrate these cells. In contrast, retinoic acid-induced differentiated derivatives of embryonal carcinoma cells were permissive for antigen expression and infectious virus production. Replication of human cytomegalovirus in human teratocarcinoma cells may therefore depend on cellular functions associated with differentiation.

Characterization of guinea pig cytomegalovirus DNA

The genome of guinea pig cytomegalovirus (GPCMV) was analyzed and compared with that of human cytomegalovirus (HCMV). GPCMV and HCMV DNAs were isolated from virions and further purified by CsCl centrifugation. Purified GPCMV DNA sedimented as a single peak in a neutral sucrose gradient and was infectious when transfected into guinea pig embryo fibroblast cells. The cytopathology was characteristic of that seen after infection with GPCMV. Virus DNA purified from virions isolated from infected GPEF or 104C1 cells had a CsCl buoyant density of 1.713 g/cm3, which corresponds to a guanine plus cytosine content of 54.1%. The CsCl buoyant density of GPCMV DNA was slightly less than that of HCMV DNA (1.716 g/cm3), but sufficiently different so that the two virus DNA peaks did not coincide. GPCMV DNA cosedimented with T4 DNA in a neutral sucrose gradient. Restriction endonuclease cleavage of GPCMV or HCMV DNAs with HindIII, XbaI, or EcoRI yielded fragments easily separable by agarose gel electrophoresis and ranging from 1.0 X 10(6) to 25.8 X 10(6) daltons. The number, size, and molarity of GPCMV DNA fragments generated by restriction enzymes were determined. Hybridization of restriction endonuclease-cleaved GPCMV DNA with radioactively labeled HCMV DNA and, conversely, hybridization of restriction endonuclease-cleaved HCMV DNA with radioactively labeled GPCMV DNA indicated sequence homology between the two virus DNAs.

Mixed infection with human cytomegalovirus and human polyomavirus (BKV)

Mixed infection, the infection of a single cell by two distinguishable viruses, has been demonstrated electron microscopically in human embryo lung (HEL) and human embryo kidney (HEK) cells infected with human cytomegalovirus (HCMV) and human polyomavirus (BKV). There was no evidence of enhancement of HCMV by BKV in either cell system; however, in HEL cells under certain conditions, HCMV enhanced the growth rate of BKV. Since both BKV and HCMV are often found in the urine of immunosuppressed patients, the enhancement of BKV by HCMV may be of clinical significance.

Structural analysis of the major immediate early gene of human cytomegalovirus

The most abundant species of human cytomegalovirus (Towne) immediate early polysome-associated RNA originates from a region of ca. 2.8 kilobases (0.739 to 0.755 map units) within the XbaI-E DNA fragment. These sequences code for a 1.95-kilobase mRNA and are referred to as immediate early coding region one (M. F. Stinski, D. R. Thomsen, R. M. Stenberg, and L. C. Goldstein, J. Virol. 46:1-14, 1983). We have utilized the nuclease mapping technique of Berk and Sharp (A. J. Berk and P. A. Sharp, Cell 12:721-732, 1977) to examine this gene in detail. Cloned fragments of human cytomegalovirus DNA, either labeled with 32P in vivo or end labeled in vitro at the 5' or 3' termini, were hybridized to immediate early polysome-associated RNA. The hybrids were treated with single-strand-specific nuclease and subjected to electrophoresis in either neutral or denaturing gels. The major transcript was shown to be a spliced molecule containing a 3' terminal exon of 1,341 nucleotides. Upstream of the major body of the mRNA are three small exon sequences of 185, 88, and 121 nucleotides. The sequence of the exons as well as the locations of the intron-exon splice junctions were determined. Based on the DNA sequence, the viral mRNA molecule has one open reading frame which begins within the second exon and extends for 491 amino acid residues. The predicted molecular weight of the polypeptide originating from this region was estimated to be 64,000. It is hypothesized that this viral gene codes for the major regulatory protein controlling transcription of the viral genome at early times. The properties of the viral gene and its protein product are discussed.

Blastogenic response of human lymphocytes to early antigen(s) of human cytomegalovirus

The lymphocytes of asymptomatic, seropositive donors demonstrated blastogenic responses to early antigens of human cytomegalovirus whether or not antibodies to early antigens were detectable. The lymphocytes of six of nine patients with active cytomegalovirus infections gave stimulation indexes of greater than or equal to 2.00 with antigens of productively infected cells, whereas only two patients demonstrated comparable stimulation indexes with early antigens. Four patients with stimulation indexes of greater than or equal to 2.00 to productively infected antigens had stimulation indexes of less than or equal to 2.00 to early antigens. Viral polypeptides with molecular weights of 83,000, 72,000, 62,000, 56,000, and 40,000 were identified in early antigen preparations.

Protein counterparts of human and simian cytomegaloviruses

Cytomegalovirus (CMV) proteins from isolates of both human (HCMV) and simian (SCMV) origin have been compared. Three classes were analyzed: the immediate-early (IE) proteins, other infected-cell-specific proteins not present in virus particles, and the proteins that constitute the mature extracellular virion. Comparisons were based on one- and two-dimensional (charge-size) separations in denaturing polyacrylamide gels, and on the selectivity of biosynthetic radiolabeling with [32P]orthophosphate and [3H]glucosamine. Results indicate that most, if not all, of the HCMV and SCMV proteins recognized, have counterparts in strain Colburn. As a group, the simian strains exhibit protein similarities that distinguish them from the human strains. Among the most diagnostic of these are the 205K and 145K virion proteins, each of which is about 7K smaller than its HCMV counterpart, and the predominant IE proteins, which are 10K to 20K (depending upon the strain) larger than their HCMV counterparts. The proteins of strain Colburn are shown to be more like those of the simian isolates than the human, and more like those of a vervet strain than rhesus. Leads provided by experiments using strain Colburn have aided in the identification of a previously unrecognized, abundant virion protein that is a principal phosphate acceptor, both in vivo and in vitro. Three additional phosphorylated proteins are identified in HCMV virions, as well as three glycoproteins. Only two HCMV strain-specific protein differences were detected by comparisons based on separation in SDS-containing polyacrylamide gels--one in the IE protein of strains Towne and Davis; the other in a virus capsid protein of strain AD169.

Microtubular reaction in human fibroblasts infected by cytomegalovirus. Brief report

By the use of indirect immunofluorescence it is shown that "early" functions of human cytomegalovirus induce a loss of microtubuli in human foreskin fibroblasts within 12 hours postinfection (p.i.) which persists until about 60 hours p.i. At later times p.i. microtubular structures are eventually reestablished. Following depression during the initial 48 hours p.i. tubulin synthesis in infected cells is significantly enhanced during the initial 48 hours p.i. tubulin synthesis in infected cells is significantly enhanced during the late phase of the infectious cycle suggesting that the mechanisms regulating tubulin synthesis are not impaired.

Organization and expression of the immediate early genes of human cytomegalovirus

The immediate early genes of human cytomegalovirus were characterized according to map location, RNA transcripts, and translation products. Three regions in the large unique component (0.709 to 0.751 map units) were transcribed in the presence of an inhibitor of protein synthesis (anisomycin). A single size class of polyadenylated mRNA, 1.95 kilobases (kb), was transcribed abundantly relative to the other size classes. The predominant 1.95-kb viral RNA was transcribed from right to left on the prototype arrangement of the viral genome and spanned a region of approximately 2.8 kb (0.739 to 0.751 map units). This mRNA codes for a 75,000-dalton protein that represents the predominant immediate early protein detected in infected cells. Immunoprecipitation of viral proteins synthesized in vitro as well as in vivo demonstrated that the predominant immediate early protein is synthesized as a protein of 75,000 daltons, but is presumably modified in vivo, resulting in a broad banding pattern ranging from 75,000 to 68,000 daltons. A different immediate early viral gene (0.732 to 0.739 map units) is transcribed from left to right at relatively low levels. The 3' ends of the above viral RNAs terminate at approximately 230 base pairs apart in the region of approximately 0.739 map units. Five RNA size classes ranging from 2.25 to 1.10 kb were detected, but the 1.75-kb and 1.40-kb RNA size classes were more abundant from this region. At least four minor proteins are coded by these mRNAs, with apparent molecular weights ranging from 56,000 to 16,500. Last, a 1.95-kb mRNA was transcribed from a third region (0.709 to 0.728 map units). This viral mRNA was present at relatively low concentration and coded for a minor protein of 68,000 daltons. Since immediate early gene expression of human cytomegalovirus is dominated by the synthesis of an mRNA from the region of 0.739 to 0.751 map units that codes for the predominant immediate early protein found in the infected cell, we hypothesize that this protein is the major regulatory protein influencing the switch from restricted to extensive transcription.

Actin distribution and synthesis in human fibroblasts infected by cytomegalovirus

"Early functions" of human cytomegalovirus were found to induce a loss of microfilaments as revealed by indirect immunofluorescence and by the use of fluorescent phalloidin. Actin synthesis in infected cultures, on the other hand, appeared to be largely unchanged as estimated from the specific radioactivity of cytoplasmic actin.

Temporal patterns of human cytomegalovirus transcription: mapping the viral RNAs synthesized at immediate early, early, and late times after infection

The transcription of the human cytomegalovirus genome was investigated at immediate early, early, and late times after infection. Viral RNAs associated with either the whole cell, the nucleus, the cytoplasm, or the polyribosomes were analyzed. At immediate early times, i.e., in the absence of de novo viral protein synthesis, the viral RNA in high abundance originated from a region of the long unique section of the prototype arrangement of the viral genome (0.660 to 0.770 map units). The viral RNA in low abundance originated from the long repeat sequences (0.010 to 0.035 and 0.795 to 0.825 map units) and a region in the long unique section (0.201 to 0.260 map units). Viral RNAs associated with the polyribosomes as polyadenylated RNA were mapped to these restricted regions of the viral genome and characterized according to size class in kilobases. At 24 h after infection in the presence of an inhibitor of viral DNA replication, i.e., at early times, the stable viral RNAs in highest abundance mapped in the long repeat sequences. Viral RNAs at intermediate abundance under these conditions mapped in two regions of the long unique section of the viral genome (0.325 to 0.460 and 0.685 to 0.770 map units). Stable viral RNAs that were associated with the polyribosomes in high abundance as polyadenylated RNA orginated from the long repeat sequences, but not from the long unique section of the viral genome. An analysis of whole-cell RNA at late times (72 h) indicated that the abundant transcription was in the regions of the long unique sequences (0.325 to 0.460 and 0.660 to 0.685 map units), and transcription of intermediate abundance was from the long repeat sequences. However, stable viral mRNA's derived from the long repeat sequences were associated with the polyribosomes at late times after infection. In addition, mRNA's originating from the long and short unique sequences were found associated with the polyribosomes at higher relative concentration than at early times after infection. It is proposed that expression of the immediate early viral genes is required to transcribe the early viral genes in the long repeat and adjacent sequences. These sequences are also transcribed at late times after infection while viral DNA synthesis continues. The expression of viral genes in most of the long and short unique sequences appears to require viral DNA replication.

The virus susceptibility of skin-derived fibroblasts from families with insulin-dependent diabetes mellitus

We have studied the growth of eight different viruses on skin fibroblasts from three families each having one or more diabetic members and appropriate controls. The haplotypes of all of the family members had been previously characterized. In addition, we have investigated the growth of mumps virus on the lymphoblast cultures from four families of the same type. Our results show no difference between the growth of these viruses in cells derived from juvenile diabetics and cells derived from nondiabetic siblings and parents even when the haplotypes were identical. However, we noted a striking resistance of human skin fibroblast cultures from both normal and diabetic individuals to Coxsackie B virus infection.

Temporal regulation of human cytomegalovirus transcription at immediate early and early times after infection

The immediate early transcripts of human cytomegalovirus originated from restricted regions of the viral genome. In contrast, transcription at early times was complementary to all regions of the viral genome that were fractionated by restriction endonuclease treatment followed by agarose gel electrophoresis. The viral genome was also extensively transcribed when 2 h of protein synthesis or longer was permitted after infection in permissive cells treated with an inhibitor of viral DNA replication or in nonpermissive cells of animal origin that permit little or no viral DNA replication. The size and in vitro translation products of the cytomegalovirus-specified mRNA's at immediate early and early times after infection were determined. Discrete size classes of virus-specified polyadenylated RNA accumulated on the polyribosomes of cells infected in the presence of an inhibitor of protein synthesis. When 2 or 24 h of protein synthesis occurred after infection, there were changes in the relative abundance of the virus-specified RNAs that accumulated on polyribosomes. Treatment of nonpermissive cells had little effect on the size classes of viral RNA found associated with the polyribosomes at early times after infection. These viral mRNA's were assumed to represent early viral gene expression. In vitro translation of the viral mRNA isolated from polyribosomes at immediate early and early times after infection identified many of the virus-specified gene products and demonstrated (i) a switch from immediate early to early viral gene expression and (ii) a prolonged phase of early viral gene expression. The data also indicated that the initiation of viral RNA synthesis does not depend on the formation of viral protein, but that de novo viral protein synthesis may influence the extent of transcription of the viral genome.

Application of a human osteogenic sarcoma cell culture for detection of human cytomegalovirus antibody by immunofluorescence tests

A human osteogenic sarcoma cell culture is useful in the immunofluorescence serological test for detecting human cytomegalovirus antibody. These sarcoma cells are chronically infected with human cytomegalovirus and provide a constant number of immunofluorescence-positive cells.

Demonstration of IgG EA (early antigen) and IgM MA (membrane antigen) antibodies in CMV infection of healthy infants and in those with liver disease

The sequence of antibody production to various virus-specific antigens in CMV infection in infancy was studied. In healthy infants, IgG EA antibody was demonstrated in 18% of cord sera, and disappeared within two months after birth in all cases not shedding virus. The nonmaternal EA antibody was produced following virus excretion and decreased rapidly following cessation of virus excretion. Thus, demonstration of EA antibody in infants after 2 months of age was found to indicate acquired CMV infection, even when CMV could not be isolated. IgM MA antibody did not persist as long as EA antibody, disappearing before cessation of virus excretion. Both IgG EA and IgM MA antibodies were more frequently demonstrated in infants with hepatitis than in healthy infants. These findings suggest the possible association of CMV with hepatitis in infants.

DNA synthesis in chromatin preparations from human fibroblasts infected by cytomegalovirus

Chromatin prepared from (14C)-thymidine pulse labelled cytomegalovirus-infected human fibroblasts 72 hours postinfection exhibited under appropriate conditions endogenous activity of (3H)-thymidine triphosphate incorporation which was relatively salt-resistant and phosphonoacetic acid-sensitive. Isopycnic centrifugation of the doubly labelled DNA in CsCl revealed that cell-free incoporation occurred into viral as well as into host cell DNA. Density labelling experiments with bromodeoxyuridine triphosphate suggested the incoporation into viral DNA to be due to replicative DNA synthesis. Chromatin from infected cells contained, in addition to cellular, viral DNA polymerase activity.

Unimpaired histone synthesis in human fibroblasts infected by human cytomegalovirus

Serum-starved human foreskin fibroblasts were infected by human cytomegalovirus (Towne strain) that is thought to induce DNA replication in host cells during lytic infection. At various times postinfection, the cultures were pulse labeled with either 3H-thymidine or 14C-thymidine and 3H-lysine to examine DNA synthesis and histone synthesis, respectively. Isopycnic centrifugation of labeled DNA in CsCl revealed that precursor incorporation into host-cell DNA was enhanced over the control around 24 h postinfection and decreased after onset of viral DNA synthesis which reached a peak around 72 h postinfection. For analysis of histones 3H-lysine-labeled proteins of lysates of unfractionated cells and of chromatin preparations were subjected to polyacrylamide gel electrophoresis in presence of sodium dodecyl sulfate and subsequent fluorography. Comparison of the fluorograms from the various pulses postinfection suggested that 3H-lysine incorporation into histones exhibited no major variations concurrent with the changes of host-cell DNA synthesis. In contrast, herpes simplex virus type 1 was found progressively to extinguish histone synthesis in the course of the cellular infection. Furthermore, histone synthesis in phosphonoacetic acid-treated cytomegalovirus-infected cultures was not enhanced over that in mock-infected controls. These observations do not support the view that human cytomegalovirus induces host-cell DNA replication under the conditions used.

Human cytomegalovirus-induced immediate early antigens: analysis in sodium dodecyl sulfate-polyacrylamide gel electrophoresis after immunoprecipitation

Immediate early antigen (IEA) induced in human lung fibroblasts by human cytomegalovirus was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis after immunoprecipitation with IEA-positive human sera. Two polypeptides of 76,000 daltons (76K) and 82K were detectable within 90 min after infection. Polypeptides of similar molecular weight were also found in immunoprecipitates of human cytomegalovirus-infected cells nonpermissive for virus replication. IEA is located within the nucleus, although some of the 76K material appears to be located on the outer nuclear membrane. Raising salt concentrations in the extraction buffer increased antigen extraction. The contribution of these IEA polypeptides to IEA nuclear fluorescent staining is discussed.

Persistence of the cytomegalovirus genome in human cells

A small percentage of human fibroblast cells survived high-multiplicity infection by cytomegalovirus and were isolated as persistently infected cultures. Approximately 30% of the cells were in the productive phase of infection, since virus-specific structural antigens and virions were associated with these cells. The remaining cells contained neither viral structural antigens nor particles. Nuclear DNA from these nonproductive cells contained approximately 120 genome equivalents of viral DNA per cell as determined by reassociation kinetics. In situ hybridization confirmed that nuclei from nonproductive cells contained a significant amount of viral DNA that was distributed in most of these cells. Early virus-induced proteins and antigens were also detected. Nonproductive cells continued to grow, and there was a slow, spontaneous transition of some of these cells to productive viral replication. The majority of the viral DNA in nonproductive cells persisted with restricted gene expression. When infectious virus production was eliminated by growing the persistently infected cultures in the presence of anticytomegalovirus serum, approximately 45 genome equivalents of the viral DNA persisted per cell. The reassociation reaction approached completion. After removal of the antiserum and subculturing, infectious virus production resumed. Therefore, it was assumed that all sequences of the viral genome remained associated with these cells. Restriction of cytomegalovirus gene expression in persistently infected cell cultures is discussed.

Production of plasminogen activator by human and hamster cells infected with human cytomegalovirus

Plasminogen activator was produced by both human embryo fibroblasts (a permissive system) and hamster embryo fibroblasts (a nonpermissive system) after exposure to human cytomegalovirus. The level of this activator was measured by using plates coated with [125I]fibrin. The production of plasminogen activator was enhanced when the human cells were exposed to human cytomegalovirus previously irradiated with UV light (5,520 to 55,200 ergs/mm2).

DNA of human cytomegalovirus: size heterogeneity and defectiveness resulting from serial undiluted passage

The majority of DNA molecules associated with plaque-purified, low-multiplicity-passaged human cytomegalovirus (Towne strain) had a molecular weight of approximately 150 x 10(6) and a molecular complexity of approximately 140 x 10(6). Serial high-multiplicity passage resulted in the production of defective cytomegalovirions. An accumulation of smaller DNA molecules packaged into virions was directly correlated with a decrease in infectivity and an increase in the particle-to-PFU ratio. The majority of defective DNA molecules had a molecular weight of approximately 100 x 10(6). In addition, there were some viral DNA molecules of approximately 60 x 10(6). Restriction enzyme analysis of defective cytomegalovirus DNA detected unique DNA fragments, suggesting a specific alteration in the nucleotide sequence. Some reasons for the generation of defective cytomegalovirus DNA are discussed.

Antibody reactivity to human and vervet cytomegalovirus early antigen(s) in sera from patients with active cytomegalovirus infections and from asymptomatic donors

Human fibroblasts were infected with vervet cytomegalovirus (VCMV) and cultured in medium containing 50 micrograms of cytosine arabinoside per ml for 72 h. Early antigens (EAg) were detected in the nuclei of infected cells by an indirect fluorescent antibody test with human sera having antibody to EAg of human cytomegalovirus (HCMV). Sera from patients with serological and/or virological evidence of active HCMV infection and from asymptomatic blood donors were examined for antibody activity with the HCMV and VCMV EAg's. The HCMV and VCMV EAg's were comparable in detecting levels of antibody activity and fluctuations in antibody titer of paired sera from patients. A total of 81% of patient sera reactive with HCMV EAg were also reactive with VCMV EAg. In contrast, only 14% of the asymptomatic donor sera reactive with HCMV EAg were also reactive with VCMV EAg. The VCMV EAg, therefore, appeared to differentiate latent from active infections in humans more effectively than did HCMV EAg.

Sequence of protein synthesis in cells infected by human cytomegalovirus: early and late virus-induced polypeptides

At least 10 distinct early virus-induced polypeptides were synthesized within 0 to 6 h after infection of permissive cells with cytomegalovirus. These virus-induced polypeptides were synthesized before and independently of viral DNA replication. A majority of these early virus-induced polypeptides were also synthesized in nonpermissive cells, which do not permit viral DNA replication. The virus-induced polypeptides synthesized before viral DNA replication were hypothesized to be nonstructural proteins coded for by the cytomegalovirus genome. Their synthesis was found to be a sequential process, since three proteins preceded the synthesis of the others. Synthesis of all early cytomegalovirus-induced proteins was a transient process; the proteins reached their highest molar ratios before the onset of viral DNA replication. Late viral proteins were synthesized at the time of the onset of viral DNA replication, which was approximately 15 h after infection. Their synthesis was continuous and increased in molar ratios with the accumulation of newly synthesized viral DNA in the cells. The presence of the amino acid analog canavanine or azetadine during the early stage of infection suppressed viral DNA replication. The amount of viral DNA synthesis was directly correlated to the relative amount of late viral protein synthesis. Because synthesis of late viral proteins depended upon viral DNA replication, the proteins were not detected in permissive cells treated with an inhibitor of viral DNA synthesis or in nonpermissive cells that are restrictive for cytomegalovirus DNA replication.

Human cytomegalovirus genome: partial denaturation map and organization of genome sequences

Contour-length measurements of both nondenatured and partially denatured DNA from purified extracellular human cytomegalovirus indicate that more than one size class of viral DNA is encapsidated. In addition to a size class averaging about 100 x 10(6) daltons, a much less abundant class of larger viral DNA molecules, 150 x 10(6) to 155 x 10(6) daltons, was extracted from purified extracellular virus. As predicted by melting-curve analysis, partial denaturation of human cytomegalovirus DNA generates denaturation maps showing distinctive adenine plus thymidine (A+T)-rich and guanine plus cytosine (G+C)-rich localizations. Alignment of partial denaturation maps of both 100 x 10(6)- and 150 x 10(6)- to 155 x 10(6)-dalton molecules from maximum overlap of common A+T- and G+C-rich zones clearly shows six unique zones contained in a length equal to the longest class, 150 x 10(6) to 155 x 10(6) daltons. However, various alignments of the smaller class of the molecules within the confines of the approximately 100 x 10(6)-dalton-length equivalent are nondistinctive. Of the six unique A+T- and G+C-rich zones, five are linked in a specific sequence and maintain the same relative orientation; these features indicate the absence of major inversions within these zones. The sixth unique zone may occur at either end of this five-zone series, but it was never found at both ends of the same molecule. Additionally, this terminal zone appears to undergo complete inversions at least at one end of the alignment, and perhaps at both. These data indicate that 150 x 10(6)- to 155 x 10(6)-dalton molecules comprise human cytomegalovirus-specific genetic information.

Stimulation of cellular thymidine kinases by human cytomegalovirus

Thymidine kinase (TK) activity in WI-38 and MRC-5 human fibroblasts was analyzed by discontinuous polyacrylamide gel electrophoresis (disc-PAGE) and discontinuous glycerol gradient electrophoresis (disc-GEP) after subculture or human cytomegalovirus (HCMV) infection. Two peaks of TK activity with different relative fraction-of-migration (R(f)) values were resolved by disc-PAGE or disc-GEP in extracts from log-phase and infected cells. Growing WI-38 cells expressed a slowly migrating (R(f) = 0.14 PAGE, R(f) = 0.4 GEP) peak of TK activity, which was partially inhibited by 1.0 mM dCTP, but which retained little activity at pH 4.5. Growing MRC cells also displayed a slowly migrating peak (R(f) = 0.10 PAGE) with similar properties. Both cell types expressed a faster-migrating TK activity (R(f) = 0.45 PAGE, R(f) = 0.7 GEP) in the growing and resting state that was strongly inhibited by 1 mM dCTP but retained 50% activity at pH 4.5. When either cell type was infected with HCMV, there was a rapid and high-level stimulation of the slowly migrating form of TK and a slight stimulation of the faster-migrating form. Two strains of HCMV (AD169 and Town) failed to produce an electrophoretically distinct virus TK in either cell type after infection. TK enzymes were partially purified by disc-GEP from extracts of log-phase WI-38 or AD169-infected WI-38 cells. Characterization of these enzymes with respect to phosphate donor specificity, pH optima, thermostability, and salt inhibition showed the HCMV-stimulated TKs to be of cellular origin.

Synthesis of proteins and glycoproteins in cells infected with human cytomegalovirus

In cytomegalovirus-infected cells, the rate of protein synthesis was detected as two peaks. One occurred during the early phase of infection, 0 to 36 h postinfection, and the other occurred during the late phase, after the initiation of viral DNA synthesis. Double-isotopic-label difference analysis demonstrated that host and viral proteins were synthesized simultaneously during both phases. In the early phase, approximately 70 to 90% of the total proteins synthesized were host proteins, whereas approximately 10 to 30% were viral, even at a multiplicity of infection of 20 PFU/cell. Virus-related proteins or glycoproteins were referred to as infected-cell specific (ICS). Two ICS glycoproteins (gp145 and 100) were clearly detectable and were synthesized preferentially in the early phase of infection. Their synthesis was concomitant with stimulation of the protein synthesis rate. In the late phase of infection, approximately 50 to 60% of the total protein synthesis was viral and approximately 40 to 50% was host. The ICS proteins and glycoproteins detected during the late phase of infection were viral structural proteins. Infectious virus was not detectable until 48 to 72 h postinfection. An inhibitor of viral DNA synthesis, phosphonoacetic acid, prevented the appearance of the late-phase ICS proteins and glycoproteins, but there was little or no effect on early ICS glycoprotein synthesis. Radiolabeled ICS proteins and glycoproteins were identified by their relative rates of synthesis, by their different electrophoretic mobilities compared with those of host proteins and host glycoproteins, and by their similar electrophoretic mobilities compared to those of proteins and glycoproteins associated with virions and dense bodies of cytomegalovirus. Structural viral antigens in the infected-cell extracts were removed by immunoprecipitation, using F(ab')(2) fragments of cytomegalovirus-specific antibodies, and identified as described above. The last two criteria were used to identify viral structural ICS proteins and glycoproteins. Although approximately 35 structural proteins were found to be associated with purified virions and dense bodies, the continued synthesis of host cell proteins complicated their identification in infected cells. Nevertheless, seven of the nine structural glycoproteins were identified as ICS glycoproteins.

Antisera to human cytomegalovirus produced in hamsters: reactivity in radioimmunoassay and other antibody assay systems

Hamsters immunized with human cytomegalovirus (CMV) concentrated and purified by polyethylene glycol precipitation and density gradient centrifugation produced antisera with high titers of specific viral antibody, and which showed no significant reactivity with human host cell components. The antisera had high titers of CMV antibody in complement fixation, indirect fluorescent-antibody (FA), and neutralization tests, but titers obtained by indirect radioimmunoassay (RIA) were markedly higher. The antisera were used to follow the development of CMV antigen in infected host cells by indirect RIA and indirect FA staining. Virus-specific antigen was first detectable by RIA at 8 h after infection, and by FA staining at 16 h; cells contained optimal amounts of antigen for RIA and FA assays at 72 to 100 h postinfection. Immune globulins from the antisera were labeled with 125I for use in direct RIA. The labeled globulins gave highly specific reactions with CMV-infected cells, including those infected with low-passage isolates, and showed no reactivity with cells infected with other human herpesviruses or certain other human viruses.

Induction of alpha type DNA polymerases in human cytomegalovirus-infected WI-38 cells

Productive infection of WI-38 cells with human cytomegalovirus (HCMV) induced the increase in the activity of DNA polymerases as well as the synthesis of viral and cellular DNA. Sedimentation analyses in sucrose gradients of high ionic strength showed that the HCMV infection caused marked increase in the activity of alpha-type polymerases (resolved into alpha1, 8 S, and alpha 2, 6 S, in the present experiments), while the infection little affected the level of beta-type polymerase (about 3.5 S) activity in both the nuclei and cytoplasm. Such increase in alpha-type polymerases was also observed when DNA synthesis in WI-38 cells was enhanced by SV40 infection or by an increased concentration of serum in medium. Phosphonacetate, which selectively blocked the synthesis of HCMV DNA, did not significantly affect the HCMV-mediated induction of DNA polymerases. However, phosphonoacetate added in the reaction mixture for DNA polymerase assay inhibited the activity of the HCMV-induced polyperase alpha, but not of the polymerases alpha2 and beta. These results support the idea that alpha-type polymerases are involved in the replicative synthesis of cellular and viral DNA.

Comparative activity of immunofluorescent antibody and complement-fixing antibody in cytomegalovirus infection

Three different tests for detection of antibodies to human cytomegalovirus (CMV), complement fixing with antigen prepared by freeze-thaw disruption (CF-FT) or with antigen prepared by extraction with alkaline glycine buffer (CF-GE) and immunofluorescent staining (FA), were compared in renal transplant recipients and their healthy donors, FA and CF-GE tests yielded positive results at an identical and significantly higher frequency than CF-FT in both donors and recipients. CF-GE and FA performed on donors and recipients predicted all virus shedding post-transplant, whereas CF-FT did not. In the individuals who developed primary infection concurrent with the transplanted kidney, FA developed earlier than other antibodies in about one-half and at the same time in the remainder. In addition, the FA test could be completed more quickly and all sera could be interpreted, which made the FA test more useful than the CF-GE, but both of these tests were clearly superior to CF-FT.

Human cytomegalovirus: glycoproteins associated with virions and dense bodies

The glycoproteins associated with the membranes of cytomegalovirions and dense bodies were characterized by their relative mobility, percentage of glucosamine incorporation, and molecular weight. Eight glycopolypeptides were repeatedly detectable. Three glycopolypeptides of higher molecular weight with low levels of glucosamine incorporation were occasionally detectable. These latter glycopolypeptides may be precursors or aggregates of the glycopolypeptides with lower molecular weights. The glycoproteins associated with the membranes were on the surface, as determined by iodination with 125I of virions and dense bodies partially purified in gradients of D-sorbitol. Velocity centrifugation in linear gradients of D-sorbitol was used to obtain concentrated and partially purified preparations of infectious cytomegalovirus. Viral infectivity and the membranes of cytomegalovirions and dense bodies were stable in gradients of sorbitol, but cellular contaminants were not completely removed. Additional centrifugation in CsCl separated both cellular contaminants and viral nucleocapsids from virions and dense bodies. Many dense bodies, which are considered to be aberrant forms of cytomegalovirus, had the same size, sedimentation properties, and density as virions. Consequently, they were not separable from virions by various centrifugation techniques. Electron microscopy demonstrated that purified virions and dense bodies were qualitatively free of extraneous material and that each dense body was bounded by a membrane, as evidenced by its double-tract appearance. Antisera to a preparation of purified virions and dense bodies, or to their glycoproteins, contained antibodies that neutralized viral infectivity and reacted with antigens in cells infected with cytomegalovirus. However, these same antisera did not contain antibodies that reacted with uninfected cells. The glycoproteins associated with the membranes of cytomegalovirions and dense bodies are considered to be specified by the cytomegalovirus genome.

Plaque reduction neutralization test for human cytomegalovirus based upon enhanced uptake of neutral red by virus-infected cells

Foci of cells infected with human cytomegalovirus were noted to stain more intensely than uninfected cells with neutral red, and this provided the basis for development of a plaque assay and plaque reduction neutralization test for cytomegalovirus. Plaques demonstrable by neutral red staining could be counted at 8 days after infection; thus, results could be obtained earlier than for plaque assay systems based upon the viral cytopathic effect, a fewer manipulations were required for staining cell monolayers to demonstrate plaques. Certain variables affecting plaque size and numbers and antibody titers were defined. Addition of fresh guinea pig complement to the reaction mixtures markedly enhanced cytomegalovirus-neutralizing antibody titers of hyperimmune animal sera, but titers of human sera were enhanced only two-or fourfold.

Analysis of cytomegalovirus genomes with restriction endonucleases Hin D III and EcoR-1

Cleavage of genomes of eleven human, one simian, and one simian-related cytomegalovirus (CMV) isolate by the restriction endonucleases HinD III and EcoR-1 generated reproducible DNA fragments. The size range of CMV DNA fragments as estimated by contour length measurements in comparison with simian virus 40 form II DNA and by coelectrophoresis with EcoR-1 fragments of herpes simplex virus DNA varied between 15 X 10(6) and 0.5 X 10(6) daltons. Comparison of the cleavage products of each isolate in 1% agarose slab gels showed extensive comigration of fragments among the human CMV isolates. In the HinD III digests, three fragment bands comigrated among all human CMV isolates, and six fragments comigrated among most, but not all, human CMV isolates. In the EcoR-1 digests, nine fragment bands comigrated among all human CMV isolates, and five bands comigrated among most, but not all human isolates. Each isolate had a distinctive electrophoretic profile with either HinD III or EcoR-1 digests. No two isolates had identical HinD III or EcoR-1 patterns although some isolates did share more general pattern similarities than others. No clear-cut subgrouping of isolates based on cleavage pattern characteristics could be discerned. Comparison of HinD III and EcoR-1 patterns showed that human isolates differ greatly from nonhuman CMV isolates. HinD III and EcoR-1 digests of each isolate contained both major and minor molar classes of DNA fragments that ranged from about 1 and multiples of 1 M down to about 0.25 M; however, the summed molecular weights for major molar fragments resulting from HinD III or EcoR-1 digests of several isolates closely approximated the molecular weight of 10(8) of the intact genome.

Detection of human cytomegalovirus and analysis of strain variation

Images

Human cytomegalovirus. IV. Specific inhibition of virus-induced DNA polymerase activity and viral DNA replication by phosphonoacetic acid

Phosphonoacetic acid specifically inhibited human cytomegalovirus DNA synthesis in virus-infected human fibroblasts as detected by virus-specific nucleic acid hybridization. Inhibition was reversible; viral DNA synthesis resumed upon the removal of the drug. The compound partially inhibited DNA synthesis of host cells in the log phase of growth but had little effect on confluent cells. Studies of partially purified enzymes indicated that phosphonoacetic acid specifically inhibited virus-induced DNA polymerase and had only a slight effect on normal host cell enzymes. The drug was shown to interact directly with virus-induced enzyme but not with the template-primers.

Transmission of cytomegalovirus infection with renal allograft

Fifty-four patients who received a renal allograft between October 1971 and October 1974 were followed prospectively to correlate pretransplant serum antibody to cytomegalovirus (CMV) with shedding of CMV following transplantation. Twenty-five of 54 patients had antibody demonstrable to CMV using immunofluorescent techniques, but only 20 of 54 using complement-fixing techniques. All 24 who had antibody and survived one month or longer, and seven of nine without antibody but who received a kidney from a seropositive donor shed virus after transplantation, whereas none of 12 individuals without antibody and who received a kidney from a seronegative donor (P less than 0.005) shed virus. Three of eight other seronegative patients for whom donor sera were not available for analysis shed virus. Viremia occurred in eight of ten individuals who developed new antibody after transplantation, versus seven of 24 with antibody prior to transplant (P less than 0.02), and virus shedding in seroconverters from other sites was significantly more persistent than in pretransplant antibody-positive patients. Thus, CMV infection was due either to reactivation of latent infection or was transmitted along with the renal allograft and manifested as a primary infection.

Demonstration of immunoglobulin G receptors induced by human cytomegalovirus

Human cytomegalovirus induced a new immunoglobulin G receptor in human fibroblasts. The immunoglobulin G receptor was well localized in the perinuclear region at 48 h postinfection, and antiviral agents blocked its synthesis. The immunoglobulin G receptor bound immunoglobulin G of man and several other species. It may be a source of error in the performance of indirect fluorescence tests for human cytomegalovirus antibody.