Effect of inhibitors of the host cell RNA polymerase II on African swine fever virus multiplication

The role of the host cell RNA polymerase II in African swine fever (ASF) virus growth has been examined using inhibitors of this enzyme. The adenosine analog 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), an inhibitor of mRNA precursor synthesis in mammalian cells, strongly inhibits the production of infectious progeny virus in Vero cells, but does not significantly affect the synthesis of virus-specific macromolecules. On the other hand, virion assembly seems to proceed normally in the presence of DRB, as virus particles can be seen in electron micrographs with a morphology indistinguishable from that observed in the absence of the inhibitor. However, taking into account the inhibition of the infectivity caused by the drug, most of these particles must be defective. In contrast with this effect of DRB on ASF virus replication, the toxin alpha-amanitin does not inhibit the production of infectious ASF virus in Vero cells or porcine alveolar macrophages. This result indicates that the host RNA polymerase II does not transcribe viral genes and that active transcription of the cell genome is not needed for ASF virus replication.

Synthesis of African swine fever (ASF) virus-specific antibodies in vitro in a porcine leucocyte system

We have developed a system of porcine peripheral blood mononuclear cells for the synthesis of antibodies in vitro, induced by partially purified African swine fever virus particles inactivated with formaldehyde. The antibodies synthesized were detected by a radioimmunoassay with a sensitivity of 3 ng of immunoglobulin. Primary responses were dependent on supernatants from peripheral blood mononuclear cells incubated with concanavalin A, macrophages and T lymphocytes. Secondary responses did not require concanavalin A-conditioned medium. The kinetics of antibody synthesis was similar in both primary and secondary responses, but the extent of synthesis was four to five times larger in the secondary than in the primary response. The antibodies synthesized in vitro were specific for African swine fever virus antigens (and did not react with viral antigen other than that from African swine fever virus particles), in contrast to pokeweed mitogen-induced antibodies, which reacted with all the antigens tested. African swine fever virus-induced antibodies did not neutralize the virus. These results and the inability of the virus to stimulate a primary response in the absence of concanavalin A supernatants indicate that inactivated African swine fever virus is not a polyclonal stimulator.

Glycosylated components induced in African swine fever (ASF) virus-infected Vero cells

African swine fever (ASF) virus production was inhibited more than 100 fold by 5 mM glucosamine, 2 mM 2-deoxyglucose and 3 microM tunicamycin. ASF virus induced in Vero cells the synthesis of 19 glycosylated components of molecular weights ranging from 9K to 220K, the major ones being those of 9K, 13K, 14K, 74K and 220K. At least five of the induced glycosylated components, of molecular weights 13K, 33K, 34K, 38K and 220K, were probably virus-coded glycoproteins, as suggested by a comparative analysis of the time course of synthesis and the antigenicity of these components in extracts from [35S]methionine or [14C]glucosamine-labeled infected cells. The non-protein glycosylated components present in extracellular ASF virus particles had a cellular origin.

Hairpin loop structure of African swine fever virus DNA

The ends of African swine fever virus genome are formed by a 37 nucleotide-long hairpin loop composed, almost entirely, of incompletely paired A and T residues. The loops at each DNA end were present in two equimolar forms that, when compared in opposite polarities, were inverted and complementary (flip-flop), as in the case of poxvirus DNA. The hairpin loops of African swine fever and vaccinia virus DNAs had no homology, but both DNAs had a 16 nucleotide-long sequence, close to the hairpin loops, with an homology of about 80%. An analysis of African swine fever virus replicating DNA showed head-to-head and tail-to-tail linked molecules that may be replicative intermediates.

African swine fever virus-induced polypeptides in Vero cells

African swine fever virus induces in Vero cells 81 acid and 14 basic polypeptides which account for most of the information content of the virus DNA. The kinetics and the cytosine arabinoside sensitivity of the synthesis of the virus-induced polypeptides showed the existence of three classes of proteins, two early and one late. Most of the early proteins were synthesized along the whole replication cycle, but the synthesis of some of the early proteins was switched-off after virus DNA replication. Late proteins were defined as those whose synthesis did not take place in the presence of cytosine arabinoside. Cell iodination with chloramine T showed the presence in the membrane of the infected cells of two major virus-induced proteins of relative molecular weights 220K and 32K. Protein p220 was incorporated into the membrane very soon after its synthesis, before the appearance of intracellular infectious virus, whereas in the case of protein p32 there was a delay between synthesis and incorporation into the membrane.

Glycosylated components of African swine fever virus particles

Extracellular African swine fever (ASF) virus particles were specifically agglutinated by several lectins, suggesting the presence of surface glycosylated component(s) containing at least glucose, mannose, or both; galactose, N-acetylgalactosamine, or both; N-acetylneuraminic acid and N-acetylglucosamine, but not fucose. When virions were purified from infected Vero cells labeled with [14C]glucosamine, [14C]galactose and analyzed by polyacrylamide gel electrophoresis, no major structural glycoproteins were detected. However, several species of glycolipids were found when virions were extracted with organic solvents and analyzed by thin layer chromatography. These, plus two minor glycosylated structural components, of apparent mol wt 230K and 95K, could account for the agglutination of ASF virions with concanavalin A.

Transcription and translation maps of African swine fever virus

A transcription map of African swine fever (ASF) virus DNA was obtained by hybridization of 32P-labeled early and late RNAs synthesized in Vero cells infected with ASF virus to dot-blots containing cloned restriction fragments spanning the viral genome. Early RNAs synthesized in infected cells in the presence of protein or DNA synthesis inhibitors hybridized preferentially to four regions in the genome, with coordinates E1 (0-51.9 kbp), E3 (63.7-75.2 kbp), E5 (100.1-111.6 kbp), and E7 (150-170 kbp). Late RNA present in infected cells after DNA replication hybridized with essentially all the genome. The RNA synthesized in vitro by the RNA polymerase associated with ASF virions hybridized to the same DNA regions than early RNA. After hybridization selection with DNA restriction fragments and translation in reticulocyte lysates the RNA synthesized in vitro produced the same proteins as early RNA. These results suggest that early RNA is synthesized in the infected cells by the virion-associated RNA polymerase. Maps of early and late proteins of ASF virus were constructed by cell-free translation of early or late RNAs selected by hybridization to cloned restriction fragments of virus DNA. About 100 early and 100 late polypeptide bands were mapped on the ASF virus genome.

Establishment of a Vero cell line persistently infected with African swine fever virus

A Vero cell line persistently infected with African swine fever virus was established by infecting the cells in the presence of 10 mM NH4Cl (Vero-P cell line). The virus derived from the Vero-P cultures infected Vero cells, and virus titers were comparable to those obtained in Vero cells acutely infected with African swine fever virus. The structural proteins of the virus from Vero-P cells were similar to those of the virus produced in lytic infections. Virus production was low when the Vero-P cells were growing logarithmically and increased considerably in confluent cultures when lysis appeared in a fraction of the cell population.

Localization of structural proteins in African swine fever virus particles by immunoelectron microscopy

Seven African swine fever virus structural proteins were localized in the virion by immunoelectron microscopy. African swine fever virus-infected cells were incubated, before or after embedding and thin sectioning, with monoclonal antibodies specific for different structural proteins, and after labeling with protein A-gold complexes, the samples were examined in the electron microscope. Proteins p14 and p24 were found in the external region of the virion, proteins p12, p72, p17, and p37 were found in the intermediate layers, and protein p150 was found in the nucleoid and in one vertex. A monoclonal antibody that recognized protein p150 as well as p220, a virus-induced, nonstructural protein, could also bind to a component present in the nucleus of both uninfected and virus-infected cells.

Purification and properties of African swine fever virus

We describe a method for African swine fever (ASF) virus purification based on equilibrium centrifugation in Percoll density gradients of extracellular virions produced in infected VERO cells that yielded about 15 +/- 9% recovery of the starting infectious virus particles. The purified virus preparations were essentially free of a host membrane fraction (vesicles) that could not be separated from the virus by previously described purification methods. The purified virus sedimented as a single component in sucrose velocity gradients with a sedimentation coefficient of 3,500 +/- 300S, showed a DNA-protein ratio of 0.18 +/- 0.02 and a specific infectivity of 2.7 X 10(7) PFU/micrograms of protein, and remained fully infectious after storage at -70 degrees C for at least 7 months. The relative molecular weights of the 34 polypeptides detected in purified virus particles ranged from 10,000 to 150,000. Some of these proteins were probably cellular components that might account for the reactivity of purified virus with antiserum against VERO cells.

Monoclonal antibodies specific for African swine fever virus proteins

We have obtained 60 stable hybridomas which produced immunoglobulins that recognized 12 proteins from African swine fever virus particles and African swine fever virus-infected cells. Most of the monoclonal antibodies were specific for the three major structural proteins p150, p72, and p12. The specificity of some monoclonal antibodies for the structural proteins p150 and p37 and the nonstructural proteins p220 and p60 indicated that proteins p150 and p220 are antigenically related to proteins p37 and p60. The association of some viral antigens to specific subcellular components was determined by immunofluorescence and analysis of the binding of monoclonal antibodies to infected cells. A host protein (p24) seemed to be associated with the virus particles.

Porcine leukocyte cellular subsets sensitive to African swine fever virus in vitro

African swine fever virus infected most, if not all, of the macrophages (monocytes) and ca. 4% of the polymorphonuclear leukocytes from porcine peripheral blood. B and T lymphocytes, either resting or stimulated with phytohemagglutinin, lipopolysaccharide, or pokeweed mitogen, were not susceptible to the virus. All of the mitogens used inhibited African swine fever multiplication in susceptible cells. The number of virus passages in vitro and the virulence degree of the virus did not affect the susceptibility of porcine B or T lymphocytes to African swine fever virus.

Molecular cloning of African swine fever virus DNA

African swine fever virus DNA (about 170 kbp) was cleaved with the restriction endonuclease EcoRI and most of the resulting 31 fragments were cloned in either the phage vector lambda WES lambda B or the plasmid pBR325. Three fragments were not cloned in those vectors, the largest fragment EcoRI-A (21.2 kbp) and the two crosslinked terminal fragments, EcoRI-K' and D'. Endonuclease SalI cut fragment EcoRI-A into three pieces which were cloned in plasmid pBR322. The two terminal EcoRI fragments were cloned after removal of the crosslinks with nuclease S1 and addition of EcoRI linkers to the fragment ends. The complete library of the cloned fragments accounted for about 98% of ASF virus genome, the missing sequences being those removed by the nuclease S1 in the process of cloning the terminal fragments.

Restriction site map of African swine fever virus DNA

Treatment of African swine fever virus DNA (about 170 kbp) with the restriction endonucleases SalI, EcoRI, KpnI, PvuI, and SmaI yielded 14, 31, 17, 13, and 11 fragments, respectively. The order of the restriction fragments produced by each nuclease was established by identifying the crosslinked EcoRI and SalI terminal fragments and then finding overlapping fragments. The five restriction fragment maps were integrated into a single map by locating SalI, KpnI, PvuI, and SmaI sites in cloned EcoRI fragments, and orienting each fragment in the overall map.

Terminal and internal inverted repetitions in African swine fever virus DNA

An electron microscopic analysis of the heteroduplexes formed by reannealing denatured terminal restriction fragments of African swine fever (ASF) virus DNA showed Y-shaped molecules with a 2.1-kilobase-pair-long double-stranded tail and two single-stranded arms. This indicated that ASF virus DNA has terminal inverted repetitions with a length of 2.1 kbp. In addition, under less restrictive hybridization conditions, most of the heteroduplexes showed a 0.13 kbp-long internal double-stranded region, separated from the long terminal repeat by a single-stranded asymmetric loop. These internal inverted repetitions did not match well, since the heteroduplexes melted under conditions where those of the terminal repetitions were stable. In the terminal fragments EcoRI-K' and D', the distance between the terminal and the internal inverted repetitions was 2.4 and 0.4 kbp, respectively.

General morphology and capsid fine structure of African swine fever virus particles

The structure of African swine fever virus particles has been examined by electron microscopy. The analysis of virions prepared by negative staining, thin sectioning, and freeze-drying and shadowing showed that the virus particle was composed of several concentric structures with an overall icosahedral shape. The inner region of the virus particles was a nucleoid that was surrounded by a membrane covered by the capsid. The capsid had side-to-side dimensions of 172 to 191 nm and was built up by capsomers arranged in an hexagonal lattice. Computer-filtered electron micrographs of either negatively stained or freeze-dried and shadowed capsids revealed capsomers with a hexagonal outline and a hole in the center. The intercapsomer distance ranged from 7.4 to 8.1 nm. The triangulation number of the capsid was estimated to be 189 to 217, indicative of 1892 to 2172 capsomers. Extracellular African swine fever virus particles had an external membrane that resembled the cytoplasmic unit membrane.

Effect of rifamycin derivatives and coumermycin A1 on in vitro RNA synthesis by African swine fever virus. Brief report

Several rifamycin derivatives inhibited the DNA-dependent RNA polymerase of African swine fever (ASF) virus particles. The inhibition was similar to that found with vaccinia virus RNA polymerase. Coumermycin A1, an inhibitor of type II DNA topoisomerases, inhibited strongly RNA synthesis in vitro by ASF virus particles. This suggests that transcription of ASF virus DNA requires a DNA topoisomerase.

Production and titration of African swine fever virus in porcine alveolar macrophages

The broncho-alveolar lavage of a pig (20-40 kg) contains about 1.6 x 10(9) alveolar cells, half of which were macrophages. The number of cells in the lavage of bacille Calmette Guerin (BCG)-treated pigs increased about 4-fold. Both African swine fever virus-infected porcine alveolar macrophages and blood monocytes produced about 1000 hemadsorption units/cell, a value 10-fold larger than that obtained in virus-infected Vero cells. Porcine alveolar cells could be stored frozen and, after thawing, they could be infected with African swine fever virus, producing the same amount of virus as the unfrozen cells. With the number of alveolar macrophages obtained from a single pit it is possible to titer about 3000 virus samples with the same stock of alveolar macrophages.

Nucleoside triphosphate phosphohydrolase activities in African swine fever virus

African swine fever virus contains nucleoside triphosphate phosphohydrolase activity which releases 32P phosphate from gamma-32P ATP at a rate of about 1 mumol/h mg of virus protein. The hydrolase activity is slightly stimulated by adding nucleic acids to the reaction mixture and under conditions of RNA synthesis. A study of the rate of ATP hydrolysis at different concentrations of ATP suggests the existence of two phosphohydrolase activities with apparent Km values of about 0.04 and 1 mM.

Comparison of the A-T rich regions and the Bacillus subtilis RNA polymerase binding sites in phage phi 29 DNA

By using a modification of the BAC spreading method for mounting the DNA for electron microscopy, partial denaturation maps of protein-free phi 29 DNA and of phi 29 DNA containing protein p3 were obtained. In phi 29 p3-DNA1 the protein does not seem to influence the melting of the ends of the molecules. The comparison of the partial denaturation map and the B. subtilis RNA polymerase binding sites indicates that five of the seven early promoters (A1, A2, A3, B2 and C2) are located in A-T rich DNA regions whereas the other two early promoters (B1 and C1) are located in less A-T rich sites.

Cross-links in African swine fever virus DNA

African swine fever virus DNA sediments in neutral sucrose density gradients as a single component with a sedimentation coefficient of 60S. In alkaline sucrose density gradients, this material shows two components with sedimentation coefficients of 85S and 95S, respectively. The sedimentation rate value of alkali-denatured virus DNA in neutral sucrose density gradients and the renaturation velocity of denatured DNA show that is reassociated much faster than expected from its genetic complexity. This behavior is compatible with the existence of interstrand cross-links in the molecule. We also present results which suggest that there are only a few such cross-links per molecule, that they are sensitive to S1 nuclease digestion, and that they are probably located next to the ends of the DNA.

Order of assembly of the lower collar and the tail proteins of Bacillus subtilis bacteriophage phi 29

Extracts obtained after restrictive infection of Bacillus subtilis with mutants in cistron 11 of bacteriophage phi 29 are complemented in vitro by extract donors of the lower collar protein (p11). Purified 11- heads, containing the major capsid protein (p8), the fiber protein (p8.5), the upper collar protein (p10), and the virus DNA, can be also complemented in vitro to produce infective virus. This result suggests that 11- heads are intermediates in phage phi 29 morphogenesis. The order of assembly of the lower collar protein p11 and the tail protein p9 was determined in vitro in two complementation steps. The results obtained indicate that the lower collar protein is assembled before the tail protein.

Inhibition of African swine fever (ASF virus replication by phosphonoacetic acid

Phosphonoacetic acid (PAA) inhibits the multiplication of African swine fever (ASF) virus in VERO cells. The observed inhibition of the in vivo DNA synthesis could be related to the in vitro inhibition of a virus-induced DNA polymerase activity present in cytoplasmic extracts from infected VERO cells.

Order of the two major head protein genes of bacteriophage phi 29 of Bacillus subtilis

Bacteriophage phi 29 mutation sus8(22) has been mapped by two-factor crosses between markers sus8(769) and ts8(93). Whe sus8(22) infects Bacillus subtilis su- proteins, HP1 (major head protein) and HP3 (fiber protein) are not synthesized; instead, a fragment with a molecular weight of 25,000 is produced. The tryptic peptides of the fragments overlap with corresponding peptides in protein HP1, but not with the peptides of protein HP3, showing that cistron 8 codes for the major head protein HP1.

Sensitivity of macrophages from different species to African swine fever (ASF) virus

The swine white blood cells sensitive to African swine fever (ASF) virus are monocytes differentiated in vitro to macrophages. These cells have been characterized by their morphology, phagocytic capacity and the presence of receptors for swine immunoglobulin G in their membranes. ASF virus does not produce any detectable effect on macrophages from humans, rabbits, guinea pigs, hamsters or rats, whereas ASF virus-infected chicken macrophages show an enhancement of cellular DNA synthesis and an intense cytopathic effect. ASF virus, adapted to grow in VERO cells, produces a strong cytopathic effect in human macrophages leading to cell destruction. This effect is not associated with the synthesis of infectious virus, cellular or virus DNA nor with the formation of detectable virus-related structures.

Assembly of Bacillus subtilis phage phe29. 2. Mutants in the cistrons coding for the non-structural proteins

The effect on phage morphogenesis of sus mutations in the cistrons coding for nonstructural proteins has been studied. Mutants in three cistrons analyzed that are involved in phage DNA synthesis, as well as in cistron 16 which codes for a late nonstructural protein, produce prolate capsids which are more rounded at the corners than complete phage heads and have an internal core; they contain the head proteins, the upper collar protein and protein p7, not present in mature phage particles. Mutants in cistron 7 do not produce capsids nor other phage-related structures; this result and the presence of p7 in phage capsids suggest an essential role in capsid assembly for this protein. The protein product of cistron 13 is probably needed for a stable DNA encapsulation since mutants in this cistron produce mainly DNA-free complete phage particles and only about 10% of uninfective DNA-containing complete phage. Cistron 15 codes for a late, partially dispensable, nonstructural protein which is present in the DNA-free capsids produced after infection with the delayed-lysis mutant sus14(1242), used as the wild-type control, or with mutants in cistrons 9, 11,12 and 13. Proteins p15 and p16 are probably involved in the encapsulation of viral DNA in a prohead.

Assembly of Bacillus subtilis phage phi29. 1. Mutants in the cistrons coding for the structural proteins

The effect of mutations in the cistrons coding for the phage structural proteins has been studied by analyzing the phage-related structures accumulated after restrictive infection. Infection with susmutants in cistron 8, lacking both the major head and the fiber protein, does not produce any phage-related structure, suggesting a single route for the assembly of phage phi29; infection with ts mutants in this cistron produces isometric particles. Mutants is cistron 9, coding for the tail protein, TP1, produce DNA-free prolate heads with an internal core; these particles are abortive and contain the head proteins HPO, HP1 and HP3, the upper collar protein NP2 and the nonstructural proteins p7, p15 and p16. Mutants in cistron 10, coding for the upper collar protein, NP2, produce DNA-free isometric heads also with an internal core; they contain the head proteins and the nonstructural protein p7, suggesting that this protein forms the internal core. Mutants in cistrons 11 and 12, coding for the lower collar protein, NP3, and the neck appendages, NP1, respectively, give rise to the formation of DNA-containing normal capsids and DNA-free prolate particles, more rounded at the corners than the normal capsids and with an internal core; the DNA-containing 11-particles are formed by the head proteins and the upper collar protein; the DNA-free 11-particles contain, besides these proteins, the nonstructural protein p7 and a small amount of proteins p15 and 16. The DNA-containing 12-particles have all the normal phage structural proteins except the neck appendages, formed by protein NP1; the DNA-free particles are similar to the DNA-free 11-particles. After restricitive infection mutant sus14(1241) has a delayed lysis phenotype and produces a phage burst higher than normal, after artificial lysis. It produces DNA-containing particles, identical to wild-type phage, which have all the normal phage structural proteins, and DNA-free prolate particles, more rounded at the corners than the final phage particles and with an internal core; the last particles contain the same proteins as the DNA-free 11 or 12-particles. These particles could represent a prohead state, ready for DNA encapsulation. None of the DNA-containing particles have the nonstructural proteins p7, p15 or p16, suggesting that these proteins are released from the proheads upon DNA encapsulation.

Transcription in vitro of phi29 DNA and EcoRI fragments by Bacillus subtilis RNA polymerase

EcoRI fragments A, B and C produced from linear phi29 DNA, but not D or E fragments, are transcribed by purified Bacillus subtilis RNA polymerase. The transcription of fragments A and C is initiated preferentially with GTP and to a lesser extent with ATP; the reverse happens in the case of fragment B. The dinucleotides GpU and GpA respectively, compete specifically with the incorporation of [gamma-32P]GTP directed by fragments A and C. The RNA synthesized in vitro by purified B. subtilis RNA polymerase is highly asymmetric. Most of the RNA synthesis directed by fragments A and C is early RNA. However, most of the RNA produced by fragment B is anti-late-RNA. Addition of crude extracts inhibit the transcription of fragment B but not that of fragments A and C.

Structure and assembly of phage phi29

Bacteriophage phi29 is a small, morphologically complex, virus with a DNA of molecular mass 12 X 10(6). The most likely structure of the head of phi29 consists of two fivefold symmetric end-caps based on T = 1 icosahedral symmetry, separated by an equatorial row of 5 hexamers. The eighteen genes identified in phi29 genome have been mapped and, in some cases, the gene products have been identified. Five linked genes, four coding for structural proteins (G, A, E, H) and one coding for a non-structural protein (J), are essential to determine the normal shape of the capsid. Protein pJ may be a scaffolding protein. An account of the effects of mutations in phi29 genes is given.

Physical map of bacteriophage phi29 DNA

Restriction endonuclease EcoRI cleaves linear phi29 DNA at four points yielding five fragments (A-E) of molecular weights 6.0 x 10(6), 3.8 x 10(6), 1.3 x 10(6), 0.6 x 10(6), and 0.3 x 10(6). The relative order of the fragments was shown to be A, B, E, D, C by analysis of the EcoRI partial digestion products and from the study of the fragments obtained by treatment of protein-containing DNA with EcoRI and trypsin. The EcoRI cleavage map of phi29 DNA has been ordered relative to the genetic map by marker rescue experiments.

Titration of African swine fever (ASF) virus

A haemadsorption microtest for African swine fever (ASF) virus is described. This assay is as sensitive and its response is faster than the conventional assay which uses buffy coat cultures in Leighton tubes. The method can also process a larger number of samples by using smaller amounts of swine blood and laboratory space. A plaque assay for ASF virus adapted to grow in VERO cells gives a titre similar to that obtained using the haemadsorption microtest. In both the micromethod and the plaque assay infection may be produced by a single infective particle.

Isolation and properties of the DNA of African swine fever (ASF) virus

African swine fever (ASF) virus was grown either in swine macrophages or in VERO cells and purified free of cell DNA. Virus DNA was isolated from virions as a molecule with a sedimentation coefficient of 60S and a contour of 58 +/- 3 mum. .these two values give a mol. wt. of 102 +/- 5 X 10(6) and 107 +/- 5 X 10(6), respectively, for the genome of ASF virus. Denatured DNA fragments from ASF virus reassociate with a C0t1/2 value of 0-60 +/- 0-05 MS, which compared with the corresponding value for T4 DNA gives for the molecular mass of ASF virus DNA a value of 102 +/- 8 X 10(6) daltons. Only virus DNA is synthesized ASF virus-infected swine macrophages.

Genetic analysis of bacteriophage phi 29 of Bacillus subtilis: integration and mapping of reference mutants of two collections

Reference mutants of Bacillus subtilis phage phi 29 of the Madrid and Minneapolis collections were employed to construct a genetic map. Suppressor-sensitive and temperature-sensitive mutants were assigned to 17 cistrons by quantitative complementation. Three-factor crosses were used to assign an unambiguous order for the 17 cistrons. Recombination frequencies determined by two-factor crosses were used to construct a linear genetic map of 24.4 recombination units. The genes were numbered sequentially from left to right (1 to 17) according to their relative map position.

Bacillus subtilis phage phi29. Characterization of gene products and functions

A total of 22 phi29-induced proteins have been resolved by slab gel electrophoresis; two of these proteins are the precursor and product fragment, respectively, in the synthesis of the neck appendage protein of the phage. The protein products of 10 out of the 17 cistrons detected in the genome of phage phi29 have been identified. Mutants in two other cistrons fail to synthesize two proteins. Mutants in six genes do not synthesize phage DNA. A cistron, probably involved in the final lysis of the infected bacteria, has been found. Mutants in this gene give place, under restrictive conditions, to delayed lysis and produce, after artificial lysis, a burst size similar or higher than that obtained after wild-type phage infection.

Synthesis in vitro of phi29-specific early proteins directed by phage DNA

The RNA and proteins synthesized in an Escherichia coli cell-free system of protein synthesis directed by Bacillus subtilis phage phi29 DNA were studied. Hybridization-competition experiments showed that most of the RNA species synthesized in vitro are early RNAs. Many of the early proteins induced after phage infection were also synthesized in the E. coli cell-free system. None of the late proteins, structural or non-structural, were synthesized in the system in vitro.

Proteins induced in Bacillus subtilis infected with bacteriophage phi29

Bacteriophage phi29 induces, in UV-irradiated B. subtilis, the synthesis of 12 non-structural proteins as well as the 7 structural polypeptides which form the viral particle. The molecular weight of the nonstructural polypeptides amounts to 180,000 daltons; if all these proteins are phage-coded, this corresponds to about 30% of the information content of phi29 DNA. The phage-induced polypeptides can be classified as early and late proteins, according with the time of their appearance after infection. All the structural proteins as well as three nonstructural proteins are late proteins. The remaining nonstructural proteins appear early after infection.