Isolation and characterization of deletion mutants of herpes simplex virus type 2 (strain HG52)

The herpes simplex virus virulence factor ICP34.5 and the cellular protein MyD116 complex with proliferating cell nuclear antigen through the 63-amino-acid domain conserved in ICP34.5, MyD116, and GADD34

The herpes simplex virus (HSV) virulence factor ICP34.5, the mouse myeloid differentiation protein MyD116, and the hamster growth arrest and DNA damage protein GADD34 share a 63-amino-acid carboxyl domain which has significant homologies to otherwise divergent proteins. Here we report that both ICP34.5 and its cellular homolog MyD116 complex through the conserved domain with proliferating cell nuclear antigen. In addition, HSV infection induces a novel 70-kDa cellular protein detectable by antisera to both ICP34.5 and GADD34, demonstrating that this novel protein possesses homology with the 63-amino-acid conserved domain.

A HSV-1 variant (1720) generates four equimolar isomers despite a 9200-bp deletion from TRL and sequences between 9200 np and 97,000 np in inverted orientation being covalently bound to sequences 94,000-126,372 np

The genome structure of a spontaneously generated HSV-1 strain 17 variant, 1720, has been determined by restriction endonuclease and Southern blot analysis. The short segment of 1720 is unaltered compared to the parental strain 17 genome, whereas the long segment is extensively rearranged. Almost all of TRL (approximately 9.2 kb) has been deleted and consequently IRL is converted into unique sequence. Sequences from approximately 9200 nucleotide position (np) to 97,000 np are present in inverted orientation, covalently bound to sequences in the prototype orientation from approximately 94,000 np to the L/S junction at 126,372 np. Thus, sequences from 94,000 np to 97,000 np are now diploid, with one copy in the normal orientation and location, and the other at the long terminus as an inverted repeat; no inversion of the intervening unique sequences occurs about this novel inverted repeat. In contrast, normal inversions of the long and short segments occur to give four equimolar genomic isomers, indicating that the novel long terminus has gained an "a" sequence. The duplication of sequences between 94,000 np and 97,000 np results in a genome containing two copies of UL43 and one complete and one partial copy each of genes UL42 and UL44 encoding the 65 kD DNA-binding protein and glycoprotein C, respectively. The variant has been shown to grow normally in vitro following high multiplicity infection.

Analysis of naturally occurring deletion variants of African swine fever virus: multigene family 110 is not essential for infectivity or virulence in pigs

A comparison of uncloned African swine fever virus isolates with their cloned counterparts revealed the presence of genetic variants in three out of seven uncloned field virus populations tested. Five different virus clones were isolated from the uncloned KIR69 virus stock by limit dilution. Structural analysis of the variants showed that they differed by single deletions of 10-16 kilobases in the region located between 6.8 and 27 kilobases from the left DNA terminus. There was no homology between DNA sequences immediately to the left and right of the deletions indicating that the mechanism generating deletion variants was not homologous recombination. The alignment of the restriction maps of the variants with those of other virus isolates indicated that two of the variants lacked the whole multigene family 110. This was confirmed by hybridization of the viral DNA with a degenerate oligonucleotide probe. Each virus variant replicated to high titer and was virulent in domestic pigs. Therefore, the multigene family 110 was not required for viral replication or virulence in domestic pigs. The virus variants were stable upon repeated passage in swine macrophages, indicating that the generation of variants is not a frequent genetic event in vitro.

Herpes simplex virus neurovirulence and productive infection of neural cells is associated with a function which maps between 0.82 and 0.832 map units on the HSV genome

A herpes simplex virus (HSV) intertypic recombinant (RE6) has been shown to be completely and specifically non-neurovirulent in mice. Direct intracranial inoculation of 10(8) PFU of RE6 does not result in a lethal encephalitis. Neurovirulent recombinant viruses were generated by cotransfection of RE6 DNA with DNA fragments cloned from the pathogenic HSV-1 strain 17 syn+. It was found that a 1.6-kb fragment mapping between 0.82-0.832 m.u. could restore the neurovirulent phenotype. Recombinants which incorporated at least part of this fragment were at least 100,000-fold more neurovirulent than RE6. The recombinants displayed a greatly enhanced capacity to replicate in mouse brain in vivo, but did not display enhanced replication over that of RE6 in cultured mouse cells at 38.5 degrees. Immunohistochemical analysis of infected mouse brain tissue revealed that the permissive host cell range of the recombinants was dramatically altered from that of RE6. While antigen positive cells were extremely rare in mouse brain tissue infected with RE6, the neurovirulent recombinants produced antigens in many cell types including neurons. Thus, wild-type HSV-1 sequences mapping between 0.82-0.832 m.u. can donate a highly neurovirulent phenotype to RE6.

Restriction endonuclease analysis of DNA from Chlamydia trachomatis biovars

DNA from a total of 60 Chlamydia trachomatis isolates was examined by restriction endonuclease analysis. Strains from all established biovars and serovars were tested. There was great diversity between the mouse biovar and the lymphogranuloma venereum (LGV) and trachoma biovars. The LGV and trachoma biovar isolates generated similar fragment patterns; however, distinct fragments appeared to be unique to both biovars, thus allowing differentiation of these two major groups. In most cases, strains of the same serovar could be differentiated from one another when a battery of restriction enzymes was used. In addition, in some cases, certain restriction fragments appeared to be characteristic of strains from a particular geographical location. The DNA patterns generated by all C. trachomatis isolates differed greatly from the DNA patterns generated from the Chlamydia psittaci isolates tested, including TWAR, a human C. psittaci strain.

Neurovirulence of individual plaque stocks of Herpes simplex virus type 2 strain HG 52

The virulence of ten independent plaque stocks of HSV-2 strain HG 52 was determined by intracranial inoculation of 3 week old BALB/c mice. The ten stocks exhibited a range of LD50 which could be grouped into three classes; high (less than 10(3) pfu/mouse), intermediate (10(3)-10(4) pfu/mouse) and low (greater than 10(5) pfu/mouse). Analysis of the ten stocks using six different restriction endonucleases showed no significant variation in the size and distribution of fragments. Isolates from the brains of dead mice had restriction enzyme profiles indistinguishable from the initial infecting virus. The pfu:particle ratios of the virus stocks were comparable. There were no significant differences between the single growth cycle characteristics in vitro of the parental HG 52 and the various plaque purified stocks. In vivo after intracranial inoculation the low virulence stocks grew poorly while those of high virulence grew well. Plaques were picked from the high and low virulence stocks after passage five times in vitro and re-assayed for virulence. In some cases there were differences in the LD50s of passaged plaque isolates from that of parental stock. The restriction enzyme profiles of the passaged plaque isolates remained unchanged. The analysis has clearly demonstrated virulence heterogeneity within a single HSV-2 virus stock.

Host cell-specific growth advantage of pseudorabies virus with a deletion in the genome sequences encoding a structural glycoprotein

Several attenuated strains of pseudorabies virus contain genomes that carry a deletion in their short unique (Us) component. The sizes of the deletions are different in the various attenuated strains; the deletions may include part of one of the inverted repeats as well as part of the Us region of the genome. In most cases, the deletion includes the gene encoding the glycoprotein gI. The attenuated strains with a deletion in their S component have a common history of having been cultivated in chicken embryo fibroblasts (CEF). We show here that passage of wild-type virus in CEF promotes the emergence of populations of virions with a deletion in their S component. The emergence of these mutants is the result of their growth advantage over the wild type and is related to the lack of expression of gI, as shown by the following. (i) The Norden strain (which has a deletion in the Us) was marker rescued to restore an intact Us. The nonrescued Norden strain had a growth advantage over the rescued Norden strain in CEF. (ii) Passage of wild-type (gI+) virus in CEF but not in rabbit kidney or pig kidney cells resulted invariably in the emergence of virions whose genomes had a deletion in the S component. (iii) Passage of a gI- mutant in CEF did not result in the emergence of such virions. The emergence of virions with a deletion in their S component thus appears to be linked to gI expression. We conclude that gI is deleterious to the growth of pseudorabies virus in CEF and that this effect is cell type specific.