Proposed nomenclature for mutants of adenoviruses

Genetic Analysis of Adenovirus Type 2 II. Preliminary Phenotypic Characterization of Temperature-Sensitive Mutants

The properties of temperature-sensitive mutants of adenovirus type 2 representing 12 complementation groups were studied. All mutants were normal with respect to adsorption as measured by viral inclusion formation and viral DNA synthesis as shown by velocity sedimentation in alkaline sucrose gradients. One mutant, however, formed viral inclusions of altered morphology at the nonpermissive temperature. The synthesis of the major capsid proteins was examined by immunodiffusion. On this basis, the complementation groups could be arranged as follows: (i) one group was negative for all three proteins; (ii) three groups failed to synthesize penton bases; (iii) eight groups were positive for hexons, pentons, and fibers. The assembly of virus particles at 39 C was examined by equilibrium sedimentation in CsCl; three groups were found defective, whereas two of the penton-negative groups were positive for virion production. Tests of the thermolability of virions at 50 C revealed eight groups labile whereas the remainder were insensitive to heat inactivation. None of five mutants inoculated in newborn rats induced tumors, although three of them were capable of in vitro transformation.

Development of a complementing cell line and a system for construction of adenovirus vectors with E1 and E2a deleted

Although adenovirus vectors offer many advantages, it would be desirable to develop vectors with improved expression and decreased toxicity. Toward this objective, an adenovirus vector system with deletion of both the El and E2a regions was developed. A 5.9-kb fragment of the adenovirus type 5 (Ad5) genome containing the E2a gene and its early and late promoters was transfected into 293 cells. A complementing cell line, designated 293-C2, expressed the E2a mRNA and protein and was found to complement the defect in Ad5 viruses with temperature-sensitive or deletion mutations in E2a. A deletion of 1.3 kb removing codons 40 to 471 of the 529 amino acids of E2a was introduced into plasmids for preparation of viruses and vectors. An Ad5 virus with disruption of the El gene and deletion of E2a grew on 293-C2 cells but not on 293 cells. Vectors with E1 and E2a deleted expressing Escherichia coli beta-galactosidase or human alpha1-antitrypsin were prepared and expressed the reporter genes after intravenous injection into mice. This vector system retains sequences in common between the complementing cell line and the vectors, including 3.4 kb upstream and 1.1 kb downstream of the deletion. These vectors have potential advantages of increased capacity for insertion of transgene sequences, elimination of expression of E2a, and possibly reduction in expression of other viral proteins. Although the titers of the vectors with deleted are about 10- to 30-fold below those of vectors with E2a wild-type regions, the former vectors are suitable for detailed studies with animals to evaluate the effects on host immune responses, on duration of expression, and on safety.

Physical mapping of two temperature-sensitive adenovirus mutants affected in the DNA polymerase and DNA binding protein

We have determined the exact nature of two thermosensitive (ts) adenovirus mutants, H5ts19 and H5ts149, which map to different genes in the E2 transcription unit. The H5ts19 mutation appears to stem from a single base-pair change of A-T to G-C at position 1840 (numbering as in ref. 1), corresponding to codon 154 of the gene coding for DBP. This results in a glutamine-to-arginine change in the amino-terminal domain of the protein. H5ts19 is defective in a late stage of infection, during virus assembly. This phenotype strongly differs from that described for the limited number of known DBP mutants, indicating that DBP is not only functional during DNA replication, but also plays a role in the late phase of the infection cycle. The defect of the (N group) mutant H5ts149 affects the initiation of viral DNA replication. Marker rescue experiments followed by nucleotide sequence analysis of H5ts149 DNA revealed a single point mutation in the gene coding for the Ad pol. A transition of C-G to A-T at position 7563 (numbering as in ref. 2) changes amino acid residue 411 of Ad pol, a leucine residue, to phenylalanine. This mutation is located in a region conserved among various DNA polymerases, which suggests an important role of this domain in DNA replication.

Characterization of a host range mutant of human adenovirus 12 defective in early region 1B

We isolated an adenovirus 12 early region 1B mutant (in206B) by ligation of the cleaved DNA-protein complex and transfection of human embryo kidney cells with the ligation products. By deduction from the DNA sequencing analysis, the two polypeptides (with molecular weights of 19,000 and 54,000) coded in the early region 1B were fused in this mutant to produce a large polypeptide. This mutant could replicate efficiently in 293 cells but not efficiently in KB or human embryo kidney cells. In KB cells, viral DNA replication could not be detected after infection with in206B. In human embryo kidney cells, viral DNA replication did occur, but the transition of viral mRNA patterns from early to late did not occur even after DNA replication, resulting in failure to produce the late polypeptides. These results indicate that the early region 1B products may be involved in both viral DNA replication and regulation of transcription.

Isolation of transformation-defective, replication-nondefective early region 1B mutants of adenovirus 12

We isolated three adenovirus 12 early region 1B mutants (in205B, in205C, and dl205) by ligation of the cleaved DNA-protein complex and transfection of human embryo kidney cells with the ligation products. These mutants could replicate efficiently in human embryo kidney or KB cells but showed markedly reduced transforming capacities both in vitro and in vivo. In cells infected with the mutants, the early region 1B gene was transcribed efficiently. In cells infected with in205B, the products corresponding to the early region 1B-coded 19,000-molecular-weight polypeptide was detected by in vitro translation but not immunoprecipitated extract of labeled cells. In cells infected with in205C or dl205, the products corresponding to the same polypeptide were not detected by either in vitro translation or immunoprecipitation of labeled cell extracts. The results suggest that the 19,000-molecular-weight polypeptide encoded by early region 1B is required for cell transformation but not for viral propagation.

Phenotypic characterization of adenovirus type 12 temperature-sensitive mutants in productive infection and transformation

Eleven temperature-sensitive mutants of adenovirus type 12, capable of forming plaques in human cells at 33 C but not at 39.5 C, were isolated from a stock of a wild-type strain after treatment with either nitrous acid or hydroxylamine. Complementation tests in doubly infected human cells permitted a tentative assignment of eight of these mutants to six complementation groups. Temperature-shift experiments revealed that one mutant is affected early and most of the other mutants are affected late. Only the early mutant, H12ts505, was temperature sensitive in viral DNA replication. Infectious virions of all the mutants except H12ts505 and two of the late mutants produced at 33 C, appeared to be more heat labile than those of the wild type. Only H12ts505 was temperature sensitive for the establishment of transformation of rat 3Y1 cells. One of the late mutants (H12ts504) had an increased transforming ability at the permissive temperature. Results of temperature-shift transformation experiments suggest that a viral function affected in H12ts505 is required for "initiation" of transformation. Some of the growth properties of H12ts505-transformed cells were also temperature dependent, suggesting that a functional expression of a gene mutation in H12ts505 is required to maintain at least some aspects of the transformed state.

Characterization of a variant of human adenovirus type 2 which multiples efficiently in simian cells

In a previous report (Klessig, J. Virol. 21:1243--1246, 1977), the isolation of a variant (H2hr400) of adenovirus serotype 2 (Ad2) that overcomes the block to multiplication of wild-type Ad2 in simian cells was described. H2hr400 replicates efficiently on both human and simian cells, resulting in virus yields that are comparable to those found when wild-type Ad2 infects permissive, human cells. An extensive comparison of the genome of H2hr400 with that of its parent by restriction endonuclease, electron microscopic, and hybridization analyses failed to detect any differences and excludes the possibility that simian virus 40 sequences, which in certain Ad2-simian virus 40 hybrid viruses (e.g., Ad2+ND1) allow adenovirus to multiply efficiently in simian cells, are present in H2hr400. In contrast to Ad2, H2hr400 can fully express its late genes in both simian and human cells. The mutation has been mapped by a modified marker rescue technique to the segment of the viral genome located between coordinates 59 and 80.

Characterization of a temperature-sensitive, hexon transport mutant of type 5 adenovirus

Infection of KB cells at 39.5 degrees C with H5ts147, a temperature-sensitive (ts) mutant of type 5 adenovirus, resulted in the cytoplasmic accumulation of hexon antigen; all other virion proteins measured, however, were normally transported into the nucleus. Immunofluorescence techniques were used to study the intracellular location of viral proteins. Genetic studies revealed that H5ts147 was the single member of a nonoverlapping complementation group and occupied a unique locus on the adenovirus genetic map, distinct from mutants that failed to produce immunologically reactive hexons at 39.5 degrees C ("hexon-minus" mutants). Sedimentation studies of extracts of H5ts147-infected cells cultured and labeled at 39.5 degrees C revealed the production of 12S hexon capsomers (the native, trimeric structures), which were immunoprecipitable to the same extent as hexons synthesized in wild type (WT)-infected cells. In contrast, only 3.4S polypeptide chains were found in extracts of cells infected with the class of mutants unable to produce immunologically reactive hexon protein at 39.5 degrees C. Hexons synthesized in H5ts147-infected cells at 39.5 degrees C were capable of being assembled into virions, to the same extent as hexons synthesized in WT-infected cells, when the temperature was shifted down to the permissive temperature, 32 degrees C. Infectious virus production was initiated within 2 to 6 h after shift-down to 32 degrees C; de novo protein synthesis was required to allow this increase in viral titer. If ts147-infected cells were shifted up to 39.5 degrees C late in the viral multiplication cycle, viral production was arrested within 1 to 2 h. The kinetics of shutoff was similar to that of a WT-infected culture treated with cycloheximide at the time of shift-up. The P-VI nonvirion polypeptide, the precursor to virion protein VI, was unstable at 39.5 degrees C, whereas the hexon polypeptide was not degraded during the chase. It appears that there is a structural requirement for the transport of hexons into the nucleus more stringent than the acquisition of immunological reactivity and folding into the 12S form.

Isolation and characterization of temperature-sensitive mutants of adenovirus type2

Fourteen temperature-sensitive mutants of human adenovirus type2, which differed in their plaquing efficiencies at at the permissive and nonpermissive temperatures by 4 to 5 orders of magnitude, were isolated. These mutants, which could be assigned to seven complementation groups, were tested for their capacity to synthesize adenovirus DNA at the nonpermissive temperature. Three mutants in three different complementation groups proved deficient in viral DNA synthesis. The DNA-negative mutant H2ts206 complemented the DNA-negative mutants H5ts36 and H5ts125, whereas mutant H2ts201 complemented H5ts36 only. Among the DNA-negative mutants, H2ts206 synthesized the smallest amount of viral DNA at the nonpermissive temperature (39.5 C). Data obtained in temperature shift experiments indicated that a very early function was involved in temperature sensitivity. In keeping with this observation, early virus-specific mRNA was not detected in cells infected with H2ts206 and maintained at 39.5 C. Prolonged (52 h) incubation of cells infected with H2ts206 at the nonpermissive temperature led to the synthesis of a high-molecular-weight form of viral DNA.

Characterization of an adenovirus early protein required for viral DNA replication: a single strand specific DNA binding proteins

1. The human adenoviruses types 2, 5 and 12 code for the production of a single strand specific DNA binding protein. The molecular weights of these proteins were 72,000 for types 2 and 5 and 60,000 for type 12. In all three cases proteolytic breakdown fragments of these binding proteins (48,000 MW) were also observed. 2. Analysis of the methionine containing tryptic peptides of these proteins indicate that the types 2 and 5 proteins are similar and clearly distinguishable from the type 12 protein. The peptide maps of these three viral proteins are clearly different from a similar protein found in mock infected cells. 3. Temperature sensitive mutants of type 5 (H5ts125) and type 12(H12tsA275) adenoviruses fail to produce these proteins at the nonpermissive temperature. H5ts125 infected cells grown at the permissive temperature produce a 72,000 MW protein that is thermolabile, for continued binding to DNA, when compared to type 5 wild type adenovirus 72,000 MW protein. An analysis of the phenotype of this adenovirus mutant indicates that it codes for a viral function at early times after infection that is required for viral DNA replication. 4. The in vitro translation of adenovirus specific m-RNA results in the synthesis of a small amount of a 72,000 MW protein that binds to single stranded DNA just like the authentic adenovirus DNA binding proteins produced in infected cells. 5. Adenovirus anti-Tumor antigen (T) anti-serum from hamsters carrying independently derived adenovirus tumors, have been tested for the presence of antibody to purified DNA binding proteins. One antiserum is positive for these antibodies while the other is negative. These results indicate that some, but not all, adenovirus tumors contain large enough levels of the DNA binding proteins to elicit an antibody response. 6. The type 5 adenovirus temperature sensitive mutant, H5ts125, that codes for a thermolabile DNA binding protein, was complemented or suppressed at the nonpermissive temperature, for the replication of adenovirus DNA, by SV40. SV40tsA temperature sensitive mutants, defective in SV40 DNA replication, do not suppress or complement H5ts125 at the nonpermissive temperature.

Temperature-sensitive mutants of adenovirus type 12 defective in viral DNA synthesis

Ten temperature-sensitive (ts) mutants of adenovirus type 12 which produce plaques at 31 but not at 38.5 C have been isolated after mutagenesis with nitrosoguanidine or nitrous acid. The mutants have been classified into six separate complementation groups. DNA-DNA hybridizations have shown that at 38.5 C the ts 401 and 406 mutants of groups B and E, respectively, synthesized less than 10% of the normal level of viral DNA. The two mutants were also defective in the production of late proteins at the nonpermissive temperature, as shown by fluorescent-antibody tests and analysis by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. Genetic recombination between the ts viruses 401 and 406 has been demonstrated; the recombination frequency for the wild-type virus production was 17.7%. Both mutants induced an increase in thymidine kinase activity at 38.5 C. Moreover, the two viral DNA-defective mutants shut off host DNA synthesis at the restrictive temperature. It is striking that at 38.5 C ts virus 401 transformed two to eight times more hamster cells than the wild-type virus, whereas ts virus 406 transformed at a frequency similar to the wild-type virus.