Herpesvirus saimiri strains from three DNA subgroups have different oncogenic potentials in New Zealand white rabbits.

Herpesvirus saimiri is a primate tumor virus that induces acute T-cell lymphomas in New World monkeys. Strains of this virus have been previously classified into three groups on the basis of extreme DNA variability of the rightmost region of unique L-DNA. To compare the oncogenic potentials of various strains, we inoculated New Zealand White rabbits with viruses representing groups A, B, and C of herpesvirus saimiri. The results showed that a group C strain were highly oncogenic in New Zealand White rabbits; however, group A or B viruses were not oncogenic in these rabbits. Analysis of DNAs of tumor tissues and lymphoid cell lines established from tumors showed that the viral genome exists in circular episomal form. To identify which part of the genome of the group C strain is responsible for the highly oncogenic phenotype, group B-C recombinant strains were constructed by an efficient drug selection technique. Two group B recombinant strains in which the right-end 9.2 kilobase pairs of unique DNA is replaced by group C virus DNA were oncogenic in rabbits, indicating that the rightmost sequences contribute to the oncogenic properties of the group C strain. Oncogenicity of herpesvirus saimiri has been traditionally evaluated in New World monkeys; infection of rabbits with group C strain 484-77 offers a much more accessible animal model to study the mechanism of oncogenicity of this virus.

In vitro immortalization of marmoset cells with three subgroups of herpesvirus saimiri.

Sequences within the rightmost 7 kilobases of the unique L DNA of herpesvirus saimiri are required for oncogenicity of the virus. The same DNA region has been found to be highly variable among different strains of herpesvirus saimiri. On the basis of this variability, herpesvirus saimiri strains were classified into groups A, B, and non-A, non-B. Herpesvirus saimiri strains representing the three groups were used successfully for in vitro immortalization of phytohemagglutinin-activated, interleukin 2 (IL-2)-expanded peripheral blood lymphocytes of common marmosets (Callithrix jacchus). Peripheral blood leukocytes could be immortalized from only a subset of common marmosets (5 of 13). All of the immortalized cell lines contained covalently closed circular viral DNA molecules and initially showed a low level of virus production. Cells immortalized by group A and group non-A, non-B strains did not require IL-2 in the medium. However, the only group B immortalized cell line, 473-SMHI, did not grow well in the absence of IL-2. The different characteristics of cell lines immortalized by herpesvirus saimiri strains belonging to different groups may help to elucidate some functions coded by the highly variable DNA region which is involved in the oncogenic process.

Classification of herpesvirus saimiri into three groups based on extreme variation in a DNA region required for oncogenicity.

The leftmost 7 kilobase pairs of unique sequence L-DNA of herpesvirus saimiri was found to be highly variable among different strains as determined by restriction endonuclease analysis and blot hybridization. This region in one group of viruses (group A) showed only very weak hybridization with the DNA of two other groups. Similarly, a fragment of group B hybridized to DNA of its own group much more strongly than to group A. No homology was detected within a 1.2-kilobase-pair region between strain 11 (group A virus) and strain SMHI (group B) even under reduced stringency, and the adjacent 5.5-kilobase-pair segment of the region showed only a very weak intergroup hybridization. DNA of a third group of viruses (non-A, non-B) did not hybridize significantly with cloned fragments representing the leftmost 7-kilobase-pair region of either group A or group B. Since sequences in the highly variable region are required for the oncogenicity of the virus, these results raise interesting questions regarding the origin and function of this region of the genome.

Recombinant DNA technology in adenovirus research.

A brief description of methods for cloning adenovirus genomic DNA and cDNA is presented, the use of recombinant clones in adenovirus research is illustrated by several examples, with particular emphasis on recent informations concerning the structure and function of adenovirus transforming genes.

Hind III restriction site map of the human adenovirus type 1 DNA.

The physical map of human adenovirus type 1 DNA was constructed with the Hind III restriction enzyme. Direct comparison of the DNA fragments with those of adenovirus type 2 revealed that the genome of adenovirus type 1 is 200 to 300 base pairs longer. The difference are located outside the region of the inverted terminal repetition within three distinct loci. Fragment Hind III-F of type 1 DNA which is presumed to carry all the genes responsible for in vitro transformation can be separated without considerable contamination by a single electrophoretic step.

Cloning the modification methylase gene of Bacillus sphaericus R in Escherichia coli.

The gene coding for the sequence-specific modification methylase methM . BspI of Bacillus sphaericus R has been cloned in Escherichia coli by means of plasmid pBR322. The selection was based on the expression of the cloned gene which rendered the recombinant plasmid resistant to BspI restriction endonuclease cleavage. The gene is carried by a 9 kb BamHI fragment and by a smaller 2.5 kb EcoRI fragment derived from the BamHI fragment. The Bsp-specific methylase level was found to be higher in the recombinant clones than in the parental strain. The methylase gene is probably located on the Bacillus sphaericus chromosome, and not on a plasmid known to be carried by this strain. The recombinant clones do not exhibit an BspI restriction endonuclease activity.