The gene encoding the major viral structural protein stimulates recombination in polyomavirus DNA

RmI is a chimeric DNA molecule consisting of a polyoma genome in which a partly duplicated VP1-coding region brackets an insert of murine DNA (Ins); when transfected into mouse cells, RmI recombines intramolecularly to yield infectious, unit-length, polyoma DNA. We report here that RmI encodes a polypeptide of 337 amino acids (designated VmP1) which includes the N-terminal 328 amino acids of VP1 and 9 amino acids specified by Ins. Mutating the VmP1-coding sequence strongly reduces the ability of RmI to yield polyoma DNA. In contrast, mutating the portion of the VP1-coding sequence which is not part of the VmP1-coding sequence has little or no impact on the ability of RmI to yield polyoma DNA, even though it renders such DNA noninfectious. Thus, release of polyoma DNA from RmI involves a function of VP1 distinct from that ensuring virus assembly and propagation; since VP1 can arise only after recombination has occurred, VmP1, but not VP1, could carry such a function. We suggest that VmP1 acts in concert with VP2, which we have already reported to stimulate recombination in RmI.

Involvement of minor structural proteins in recombination of polyoma virus DNA

We have previously observed that a polyoma-mouse chimeric DNA molecule (RmI) in which the murine DNA insert is flanked by directly repeated viral sequences is effectively converted into unit-length polyoma DNA upon transfection of permissive mouse cells. This intramolecular recombination event appears to be dependent on VmP1, a protein encoded by RmI which includes the 328 N-terminal amino acids of polyoma VP1, and nine amino acids of murine origin carrying the C-terminus of the protein. We report here that introducing mutations into the VP2/VP3 coding sequence reduces the ability of RmI to generate polyoma DNA, even though the same mutations seem to exert little or no effect on the ability of polyoma DNA to either replicate or accumulate inside transfected cells. A mutation affecting VP2 alone being as effective as one that affects both VP2 and VP3, VP2 appears to be playing a critical role in recombination.

Rescue of polyomavirus DNA after co-transfection of recombinant plasmids with viral DNA fragments

Plasmid DNA bearing a single copy of the mouse polyomavirus (Py) genome (template A) was transfected into murine cells together with another DNA (template B) carrying intact the viral sequence interrupted in template A. Rescue of unit-length Py DNA including markers from both templates was observed as long as the viral DNA in B overlapped that split in A by one kbp or more. Such rescue was not detectably enhanced by linearizing either or both template(s), and occurred in the absence of template replication. These findings are suggestive of an intermolecular recombination process taking place soon after transfection and starting with homologous pairing between A and B. Such pairing would facilitate removal of vector DNA from one template (A), followed by closure of the resulting break or gap through recombination with the other template (B). Since B may consist of a PCR-synthesized DNA fragment, these observations could conceivably serve as the basis for a method of generating mutant viral genomes.

An enhancer of recombination in polyomavirus DNA

Previous work from this laboratory has indicated that intramolecular homologous recombination of polyomavirus (Py) DNA is dependent upon promoter structure or function. In this report, we demonstrate that Py DNA contains not two but three binding sites for transcription factor YY1, all located on the late side of viral origin of replication (ori) and the third well within the VP1 coding sequence. This third site (Y3), which may or may not play a role in transcription regulation, is immediately adjacent to a previously described recombination hot spot (S1/S2). We found that Py replicons carrying an altered Y3 site recombined in a manner suggesting partial inactivation of the S1/S hot spot. Point mutations precluding the binding of YY1 to Y3 in vitro depressed hot spot activity in vivo; however, of the two reciprocal products reflecting recombination at this spot, only that carrying the mutated Y3 site arose at a reduced rate. These results are interpreted in light of a model assuming that recombination occurs within a transcriptionally active viral chromatin tethered to the nuclear matrix by YY1.

Quantitation of Chlamydia trachomatis by culture, direct immunofluorescence and competitive polymerase chain reaction

OBJECTIVES

Methods to quantitate Chlamydia trachomatis have never been compared although it would be relevant to periodically evaluate the sensitivity of a detection system. We compared the sensitivity and reproducibility of culture, direct immunofluorescence and the polymerase chain reaction (PCR) to quantitate C trachomatis.

METHODS

A competitive semiquantitative PCR procedure was developed. The number of inclusions in culture, particles by direct immunofluorescence and DNA copies by PCR were measured for 12 patient specimens. Variation was determined by measuring a sample 10 times for each method.

RESULTS

Patient C trachomatis major outer membrane protein gene DNA was measured semiquantitatively by amplifying together with reference DNA. DNA molecules, particles and infectious units were quantitated in clinical samples with, on average, 595 DNA molecules and 87 immunofluorescent particles observed per inclusion-forming-unit. Similar coefficients of variation (47-52%) were observed for the 3 procedures.

CONCLUSION

Competitive PCR and counting immunofluorescent particles provide reproducible and sensitive methods of quantitating C trachomatis.

A hotspot for promoter-dependent recombination in polyomavirus DNA

We have engineered polyomavirus (Py) DNA molecules carrying two large direct repeats within the late coding region, as well as a deletion encompassing the TATA box in the early promoter. Such constructs recombine less readily than a construct containing the same duplication of late sequences, but an intact early promoter. Furthermore, residual recombination in the molecules with a deletion occurs between homologous sites which differ from those used in the molecule without deletion. These findings are consistent with recombination being stimulated by transcription originating from the early promoter, rather than facilitated by the "openness" of viral chromatin undergoing transcription.

Variation outside variable segments of the major outer membrane protein distinguishes trachoma from urogenital isolates of the same serovar of Chlamydia trachomatis

OBJECTIVES--Whereas serovars A, B, Ba and C of Chlamydia trachomatis are usually associated with trachoma, two of these serovars (Ba and C) are occasionally observed in urogenital infections. Variation in the gene encoding the major outer membrane protein (MOMP) was explored to distinguish urogenital from trachoma specimens of the same serovar. METHODS--A large portion of the MOMP gene was amplified by nested PCR directly from clinical samples from trachoma or urogenital infection and the serovar of the infecting C trachomatis was determined by restriction fragment length polymorphism (RFLP). Amplified DNA from trachoma serovars B, Ba and C and from urogenital serovars Ba, C, D and E was sequenced by the dideoxy chain termination method. RESULTS--While almost identical in variable segment (VS)I, three urogenital Ba samples differed from all trachoma B and Ba samples at eight nucleotides including two sites which changed amino acids in the constant region upstream of VSI. An identical sequence in this region was observed for the reference urogenital D serovar. Variation in this same region upstream of VSI also distinguished 40% of serovar D samples from prototype D including three that were sequenced. Two urogenital C differed from trachoma C samples at four sites that changed the MOMP amino acid sequence including two changes in the constant region between VSII and III and single changes in VSII and III. On the basis of these sequence determinations, RFLP was predicted which allowed extension of these observations to 20 other urogenital Ba, 12 trachoma B or Ba, seven variant D, 12 D, four urogenital C and three trachoma C samples without further sequencing. CONCLUSION--Urogenital Ba and C samples have VSI or II and III sequences identical or very similar to trachoma strains of the same serovar, but resemble more closely other serovars in the constant regions. Urogenital serovar D samples can also be divided into two genotypes on the basis of sequence differences in the constant region preceding VSI.

Intramolecular recombination in polyomavirus DNA is a nonconservative process directed from the viral intergenic region

Previously, we have studied intramolecular homologous recombination in polyomavirus replicons under conditions allowing only one amplifiable recombination product to be generated from a single precursor molecule. In order to detect putative reciprocal product(s), we have now constructed precursor polyomavirus replicons which contain two copies, instead of one copy, of the viral intergenic region, including the origin of replication as well as both promoters. Upon transfection of mouse cells, constructs containing directly repeated intergenic regions yielded distinct amplifiable products, in number depending upon the functional integrity of both intergenic regions. Our data indicate that of two possible reciprocal products, a given precursor molecule would yield either one or the other but never both at the same time. Most striking, however, is the observation that promoter function is required for recombination, while the origin of replication function may be needed only for amplification of the recombination product once it has been formed. The data reported here confirm and extend previous data suggesting that (i) transcription is instrumental in recombination between direct repeats and (ii) nonconservative recombination involving direct repeats relies upon two promoters of opposing polarities.

Intramolecular recombination in polyomavirus DNA is controlled by promoter elements

We show here that intramolecular homologous recombination in polyomavirus (Py) DNA depends upon discrete sequence elements of the viral regulatory region which are believed to regulate transcription initiation and exert little or no cis-control over replication. Either deleting the viral early promoter (EP) or inverting the viral late promoter (LP) strongly impairs viral DNA recombination under conditions allowing viral DNA replication to proceed undisturbed. These findings suggest that bi-directional transcription proceeding from the intergenic region favors intramolecular recombination.

Sensitive detection and typing of Chlamydia trachomatis using nested polymerase chain reaction

OBJECTIVES

A method based on a nested polymerase chain reaction (PCR) was developed to detect and to type Chlamydia trachomatis from low titre samples by amplifying a large portion of the major outer membrane protein gene. The sensitivity of this procedure was evaluated in urogenital clinical samples in comparison with culture.

SPECIMENS

A series of 787 urogenital specimens, including 37 (4.7%) positive by culture, together with 227 other samples that had been found to yield less than 25 chlamydial inclusions in culture were tested.

METHODS

Samples were pelleted, resuspended in 1 mM NaOH, heated and amplified without further purification. After 40 cycles of PCR, 1 microliters of product was amplified by a further 30 cycles of PCR using a second set of primers nested within the initial pair. Positives were detected by agarose gel electrophoresis and confirmed by repeating the PCR analyses and determining the serovar of both amplified samples by restriction fragment length polymorphism.

RESULTS

Nested PCR allowed detection of 96% and culture 77% of positives with only three samples repeatedly positive by PCR but considered false positives because a different serovar was identified in the two amplifications. Of culture-positive samples with less than 11 chlamydia inclusion-forming-units 97% could be detected by nested PCR and most still gave a positive signal when diluted hundred fold.

CONCLUSIONS

Nested PCR provided the basis for a very sensitive C trachomatis detection and typing strategy. Repetition and typing positive samples facilitated detection of false-positive PCR specimens resulting from contamination of the PCR process or any reagent except the original sample.

Chlamydia trachomatis serovars in 435 urogenital specimens typed by restriction endonuclease analysis of amplified DNA

Chlamydia trachomatis serovar was determined by analysis of restriction fragment length polymorphism in the gene encoding the major outer membrane protein (MOMP) from 435 urogenital specimens. Of the specimens, 254 grew < 25 inclusions and 14 were negative in culture. Although previous studies defined serovar by epitopes or sequences representing only the four variable domains in MOMP, restriction endonuclease sites characteristic for each serovar not only within but also outside these variable domains were cataloged in this study. Novel serovars that grew poorly or not at all in vitro were not observed, and all samples proved similar or identical to one of the 15 known serovars. There was no significant difference in proportions of serovars between men and women. In women, F serovars were more frequently observed in infections with few inclusions in culture, whereas B group serovars predominated when many inclusions were observed.

The same mammalian replicon yields distinct recombination products in different cell lines

We have observed previously that some chimeric replicons inclusive of a partly duplicated polyomavirus (Py) genome yield unit-length Py DNA (P155) at high frequency when transfected into normal or Py-transformed mouse cells. We demonstrate here that one such replicon generates either P155 or illegitimate recombination products in other mouse cells, transformed by simian virus 40. Use of the polymerase chain reaction indicates that each of the illegitimate products carried a different deletion, but that all deletions mapped within a rather well defined portion of the precursor replicon. Thus, these products were organized as if two hotspots for recombination existed in the Py late-coding region, one being located within or near one of the duplicated sequences characteristic of the chimeric replicon. Since this particular hotspot has already been shown to be involved in the generation of P155, the data reported here could indicate that a single recombination mechanism can yield either homologous (P155) or illegitimate products. How the DNA interacts with certain proteins, such as papovavirus large tumor antigen, could explain why one or the other type of product is formed.

Typing Chlamydia trachomatis by detection of restriction fragment length polymorphism in the gene encoding the major outer membrane protein

A method that avoids culture was devised to determine serovars of Chlamydia trachomatis. Polymerase chain reaction was used first to amplify a part of the chlamydial genome that included the leader sequence and all four variable domains of the major outer membrane protein (MOMP) of the 15 serovars of C. trachomatis. The amplified DNA was then digested simultaneously with restriction endonucleases AluI and MspI and the resulting fragments separated on 10% polyacrylamide gels. After silver staining, a total of 13 characteristic patterns were observed for the 15 serovars, leaving two ambiguities that were resolved using alternate enzymes. Analysis of 40 clinical isolates revealed patterns indistinguishable from those of the prototype serovars including, unexpectedly, 5 Ba serovars. The same PCR procedure also allowed amplification of the MOMP gene of two avian Chlamydia psittaci and one Chlamydia pneumoniae isolates.

Alternative homologous and nonhomologous products arising from intramolecular recombination

RmI, a chimeric DNA molecule containing polyomavirus (Py) and mouse sequences, generates unit-length Py DNA via intramolecular recombination between two directly repeated viral sequences of 182 base pairs (S repeats). To analyze the contribution of the S repeats in this process, we produced mutants of RmI carrying deletions in either one or both S repeats and tested them for their ability to recombine in mouse 3T6 cells. Mutant DNAs were found to yield unit-length Py DNA as long as they carried a minimal internal homology of 40 to 50 base pairs. Unlike RmI itself, however, the mutants also gave rise to nonhomologous recombination products. These results suggest that when the generation of homologous products is hampered by a limiting homology, nonhomologous products may arise instead of homologous ones. Therefore, the initial step(s) in the mechanisms yielding the two kinds of products could be identical.

Preferred crossover sites on polyomavirus DNA

RmI is a hybrid replicon consisting of polyomavirus (Py) and mouse sequences that yields unit-length polyomavirus DNA via recombination between two directly repeated viral sequences of 182 base pairs (S repeats). To define the contribution of the S repeats in this intramolecular recombination, we derived from RmI a series of replicons containing the original S repeats as well as additional direct viral repeats which were 1 to 2 kilobases in length (L repeats). After mouse 3T6 cells were transfected with these constructs, recombination products that displayed the physical properties of homologous recombinants were detected. The structures of these recombinants indicated that whereas repeat length influences the likelihood of recombination, crossover occurs preferentially near the S repeats, provided that one of them is proximal to the viral origin of replication. This finding suggests that recombination near the S repeats depends on a process initiated near the viral origin of replication.

A substitution in a nonconserved region of polyomavirus large T antigen which causes a thermosensitive mutation

The temperature-sensitive defect of the tsP155 mutant of polyomavirus (Py) maps in the large T antigen (LT) coding sequence of a viral DNA diverging markedly from that of extensively characterized wild-types (WTs) such as A2 and CSP. We have sequenced about 600 base pairs (bp) "early" DNA encompassing the mutated site in tsP155, as well as the corresponding DNA segment from a revertant virus (RtsP155). As expected, tsP155 was found to be more closely related to CSP than to A2. Out of 3 single bp differences between tsP155 and CSP, 2 were common to tsP155 and RtsP155. The only substitution exclusive to tsP155 was a G----C transversion at bp 2658 which canceled the HaeIII site at bp 2657. Heteroduplexes inclusive of tsP155 DNA and of a 312-bp-long fragment of RtsP155 DNA yielded recombinant viruses growing under restrictive conditions whose DNAs had all regained the HaeIII site at bp 2657. These findings clearly identify the ts mutation with the tranversion at bp 2658, which is expected to change Ala 701 for a Pro in LT. We discuss this substitution in relation to the phenotype of tsP155.

Major rearrangement of cellular DNA in the vicinity of integrated polyomavirus DNA

The Cyp cell line was produced by transforming mouse embryo cells at the restrictive temperature with an early thermosensitive mutant of polyomavirus (Py). Transfer of Cyp cells to the nonrestrictive temperature causes excision to occur at a single chromosomal site carrying viral DNA, and leads to the production of infectious virus. We have attempted to elucidate the recombination event that occurred during the integration of Py DNA in this inducible line. Physical characterization of two recombinant DNAs-one selected from a genomic library of normal mouse DNA and the other constructed from the unoccupied allele of the Cyp integration site-indicates that generation of the Cyp line has involved the joining of not only viral DNA to a cellular alpha site, but also the cellular alpha site to a cellular alpha site to cellular beta site. Hence, previously described hybrid excision products from the Cyp line were made of mouse DNA segments representing two distinct cellular sites. The alpha-beta joining may play a role in the expression of integrated Py DNA.

An excision event that may depend on patchy homology for site specificity

In mouse cells transformed by a mutant polyomavirus genome, recombination between integrated viral DNA and flanking cellular DNA resulted in the excision of two readily amplifiable chimeras, designated RmI and RmII. The crossing-over that generated RmII was unique in that it involved a simple cellular sequence in which the triplet 5'-CTG-3' was repeated many times. We show that the sequence across the junction resulting from excision was identical in several molecules of RmII, as if the cross-over generating this junction always involved exactly the same two sites on the viral and cellular DNA. We also show that the cellular site mapped where the replacement of a G by an A in one of many successive 5'-CTG-3' triplets generated a homology of five nucleotides (5'-CTACT-3') with the viral site. Oligonucleotides on both sides of these sites are probably involved in matching the two DNAs prior to recombination.

Mouse cells surviving polyoma virus infection generally retain the whole viral genome

Permissive mouse 3T6 cells were exposed to polyoma virus--either wild-type or early mutant--at high multiplicities of infection. From colonies arising from surviving cells, so-called lines and clones were derived under conditions precluding superinfection. These lines and clones were examined for the presence of viral genetic information, using a variety of techniques. Two salient findings were made: most lines or clones analyzed had retained viral genetic material; generally, this material was nondefective, as evidenced by the production of virus and/or viral DNA molecules of genomic size. These findings indicate that mouse cells can survive for many generations while carrying a complete, infectious, and potentially cytocidal polyoma virus genome.

Alternative excision products originating from a single integration of polyomavirus DNA

The Cyp cell line consists of mouse cells transformed by a thermosensitive polyomavirus (Py) genome and routinely propagated at 39 degrees C. Cyp cells are readily induced to synthesize free Py DNA by being transferred to 33 degrees C. In one subclone (C12/a1/S48, or S48) of this line, such induction resulted in the intracellular accumulation of three discrete species of cyclic DNA, i.e., genomic Py DNA, RmI, and RmII. RmI and RmII are Py-mouse chimeras, each of which contains a distinct set of sequences originating from the site of integration. Conceivably, genomic Py DNA, RmI, and RmII could persist at 39 degrees C as free replicating plasmids or originate from distinct populations of cells in S48 cultures. The data indicated that all three species arise at 33 degrees C from a genetically homogeneous cell population in which neither RmI nor RmII replicates at 39 degrees C. Examination of the sequence at the viral-cellular junction unique to RmII indicated that this chimera is excised from the host chromosome through a recombination event involving a complex viral sequence and a simple cellular sequence. Therefore, RmII provides another example of precise recombination occurring between nonhomologous sequences in a mammalian cell, as already observed for RmI (B. S. Sylla, D. Huberdeau, D. Bourgaux-Ramoisy, and P. Bourgaux, Cell 37:661-667, 1984).

A mouse DNA sequence that mediates integration and excision of polyoma virus DNA

In mouse cells transformed by a temperature-sensitive polyoma virus (Py) genome, the integrated viral genome recombines with adjacent chromosomal DNA to yield a small cyclic molecule (RmI) with defined viral and cellular components. We have cloned the cellular component (Ins), determined its sequence, and examined its distribution in normal mouse DNA. The sequence of Ins displays several homologies with that surrounding the replication origin (ori) of Py or SV40 DNA.

Site-specific excision of integrated polyoma DNA

Cyp cells are permissive murine cells carrying a thermosensitive polyoma virus genome that remains integrated at 39 degrees C, but is effectively excised and replicated after transfer to 33 degrees C. In rare subclones of the Cyp line, temperature shift-down yields predominantly homogeneous populations of chimeric molecules that appear to reflect the circularization of defined segments of DNA spanning one of the junctions between the integrated viral genome and the adjacent cellular DNA. Such accurate and frequent excision requires a specific recombination mechanism. We examined both the cellular and the viral sequences that cross-over to generate one of these chimeric molecules, Rm I. The homology at the cross-over site is one of 1 or 2 base pairs at most; patches of homology, amounting in total to 19 or 20 base pairs, are found in perfect register on both sides of this site; and the two stretches of DNA that are joined to form RM I contain similar 12-14 base pair sequences (5'- CTCCTTTACAGAGG -3' and 5'- CTCCTTTCAAGG -3') in opposite orientations.

Biological properties of polyoma DNA fragments cloned in plasmid pBR322

The two HindIII fragments of polyoma virus DNA were cloned in the HindIII site of plasmid pBR322, and the biological activity of the recombinant plasmids was tested in tissue culture cells. A mixture of recombinant plasmids containing the HindIII-A and HindIII-B fragments was infectious, but only after cleavage with HindIII. Recombinant plasmids containing the HindIII-A fragment, but not those containing the HindIII-B fragment, induced the transformation of Fischer rat 3T3 cells. These findings indicate that about half of the early region of polyoma virus DNA is not essential for the initiation of the maintenance of transformation.

Induction of virus multiplication in permissive cells transformed by a temperature-sensitive polyoma virus. I. Isolation and partial characterization of survivors

A fibroblastic cell line transformed by ts-P155, an early temperature-sensitive mutant of polyoma virus, has been isolated after infection of secondary mouse embryo cells at the restrictive temperature of 39. These cells, designated Cyp, undergo a massive CPE accompanied by the production of infectious, temperature-sensitive virus when transferred to the nonrestrictive temperature of 33. Several independent clones were established from cells which survived the induction of virus multiplication occurring at 33. When routinely cultured at this temperature, these cells, termed R, displayed the growth properties of transformants and produced variable amounts of infectious, temperature-sensitive virus. This shedding of virus could not be "cured' by the addition to the culture medium of antipolyoma serum which had already been found to effectively suppress virus production in Cyp cell cultures transferred to 33. Moreover, R cells seemed to have developed a resistance to superinfection that the parent Cyp cell line did not exhibit. Therefore, virus production in R cell cultures probably reflects the occasional excision and replication of integrated viral genomes rather than a carrier state.

Virus shedding by SV40-transformed human cells

Cultures of human cells transformed by SV40 were found to release infectious virus, even after several passages in vitro. Virus shedding by these cultures did not depend on propagation of virus from cell to cell, as it was not affected by anti-SV40 antiserum that could effectively block virus propagation in acutely infected cells. Cells transformed by the 'early' temperature-sensitive mutant tsA30, and maintained at the restrictive temperature of 39 degrees, shed virus in reduced amount. Finally, xeroderma pigmentosum cells transformed by SV40 were also found to release virus, indicating that the enzymes of excision and repair of UV-induced damage to DNA probably were not involved in the molecular mechanism underlying virus shedding.

Replicating DNA of adenovirus type 2

We have investigated the nature of the DNA synthesized in KB cells 24 h after infection with adenovirus type 2 (ad. 2). Cellular DNA synthesis being strongly depressed, a new molecular form of ad. 2 DNA could be detected in such cells in addition to mature viral DNA. This new form, referred to as DNA-R, is preferentially labelled after short pulses of 3H-thymidine, while the radioactive label can be chased into mature viral DNA. The sedimentation properties of DNA-R are those expected for linear replicating molecules having 1–2 times the molecular weight of mature viral DNA. As a result of being partly single-stranded, these molecules can be separated from mature viral DNA by chromatography on benzoylated-naphthoylated DEAE-cellulose. Purified DNA-R was examined under the electron microscope and found to consist of Y-shaped molecules. Thus DNA-R has the properties expected for linear monomeric molecules of ad. 2 DNA replicating undirectionally.

A new tissue-culture system for clinical virology

A new, miniature tissue-culture system is described. It consists of an optically clear, non-toxic plastic multichambered container, mounted on a microscope slide. The completely separate chambers allow testing and control cultures to be maintained, using several cell strains. Direct observation with an inverted microscope is readily and accurately made. By removing the chambers from the slide, a permanent record can be made after staining, or immunofluorescent studies can be undertaken. Savings of space, manipulation and medium render this system particularly suitable for clinical virology.

The replication of the ring-shaped DNA of polyoma virus. I. Identification of the replicative intermediate

The replication of the ring-shaped polyoma DNA has been investigated. The replicative intermediate has been identified and characterized; it consists of molecules containing both circular and nicked strands, not longer than the strands of the DNA found in viral particles. The findings exclude certain proposed methods of replication of ring-shaped DNA and are compatible with Cairns' model.

Virus specific antigens in mammalian cells infected with herpes simplex virus

Antisera to specific proteins in herpes simplex infected cells were produced by immunization of rabbits with infected rabbit kidney cells. These antisera were highly virus specific and produced up to twelve lines in immunodiffusion tests against infected cell extracts. Acrylamide electrophoresis and immunoelectrophoresis revealed up to ten virus specific proteins of varying size.