Nucleotide sequence analysis of a 30-kilobase-pair region of human herpesvirus-6B (HHV-6B) genome and strain-specific variations in major immediate-early genes

Family saliva sharing behaviors and age of human herpesvirus-6B infection

OBJECTIVE

Transmission of human herpesvirus (HHV-6) type B is hypothesized to occur via saliva. We sought to determine whether behaviors promoting saliva sharing were associated with HHV-6B infection.

METHODS

Parents of young children participating in a natural history study of HHV-6B were asked to complete a questionnaire focused on family behaviors that result in saliva sharing.

RESULTS

Of 111 surveys, 109 (98%) were completed. Of the 109 participants, 37 (34%) were infected with HHV-6 before 1 year of age. Having older siblings (adjusted OR 4.1, 95% CI 1.5, 11.8) and receipt of parental saliva when kissed (adjusted OR 5.1, 95% CI 1.8, 14.5) were independently associated with younger age of HHV-6 infection. Dose-response relationships were demonstrated between HHV-6 infection before 1 year and both number of siblings and the frequency that the child received parental saliva when being kissed (p=0.006 and p=0.002, respectively).

CONCLUSIONS

Having older siblings and parents who shared saliva increased risk of HHV-6B acquisition in children. These data support the hypothesis that HHV-6 is transmitted primarily via saliva within families.

Genetic variations of human herpesvirus 7 by analysis of glycoproteins B and H, and R2-repeat regions

Clinical isolates of human herpesvirus 7 (HHV-7) from the saliva of healthy individual were investigated for genetic variations in the regions of two immediate-early (IE) genes, the glycoprotein B (gB) and glycoprotein H (gH) genes, and in R2-repeat. The genomic DNA of 24 isolates from citizens of Thailand, Japan, and the United States was amplified to detect size variations in the IE-1 and IE-2 loci, but none was observed, suggesting that there was no deletion or insertion in these genes, in contrast with an IE gene of human herpesvirus 6 (HHV-6). The sequences of the gB gene from isolates acquired from 5 Japanese and 8 Thai subject were then compared with those of American strains JI and RK with respect to codons that are known to differentiate gB alleles. All the isolates were found to have gB allele C except for the JI strain, which has allele F. Variability was also observed in five specific gH codons, resulting in 6 different groups. The HHV-7 isolates might be classified into two major genetic variants by combining their gB and gH allelic groupings. In the present study, only JI belonged to variant 1, while the rest of the isolates appeared to belong to variant 2. In the R2-repeat region, size heterogeneities were observed among the 24 isolates, due to different repeat numbers (17, 15, 14, 13, or 12 repeats). Therefore, we used the R2-repeat to identify the origins of isolates in a study of HHV-7 transmission, and found HHV-7 to be transmitted within a family from both mothers and fathers to their children.

Structure of transcripts and proteins encoded by U79-80 of human herpesvirus 6 and its subcellular localization in infected cells

We analyzed the U79-80 gene of human herpesvirus 6 (HHV-6), which is predicted to be a positional homolog of the UL112-113 gene of human cytomegalovirus (HCMV). The U79-80 gene encoded a family of nuclear proteins of 36, 41, 44, and 59 kDa. These proteins had common amino termini and were generated by complex alternative splicing. Transcripts from U79-80 appeared as early as 3 h postinfection and could be detected in the presence of phosphonoformate. U79-80 proteins were seen as early as 8 h postinfection and could be detected in the presence of phosphonoformate but not in the presence of cycloheximide combined with actinomycin D treatment. The U79-80 proteins were localized to the nucleus of infected cells, where they were detected as a speckled or punctuate pattern. Moreover, the U79-80 proteins colocalized with the components of the viral DNA replication machinery and appeared to distribute adjacent to or touching nuclear domain 10, where viral DNA replication occurs. From the sequence analysis of genomic DNA, the predicted amino acid similarity between U79-80 and UL112-113 was lower than between other genes, but the characteristics of the transcripts and proteins encoded by U79-80 were similar to those of UL112-113. These results suggest that the U79-80 proteins have a role in viral DNA replication and are functional homologues of the UL112-113 proteins.

Comparison of the complete DNA sequences of human herpesvirus 6 variants A and B

Human herpesvirus 6 (HHV-6), which belongs to the betaherpesvirus subfamily and infects mainly T cells in vitro, causes acute and latent infections. Two variants of HHV-6 have been distinguished on the basis of differences in several properties. We have determined the complete DNA sequence of HHV-6 variant B (HHV-6B) strain HST, the causative agent of exanthem subitum, and compared the sequence with that of variant A strain U1102. A total of 115 potential open reading frames (ORFs) were identified within the 161,573-bp contiguous sequence of the entire HHV-6 genome, including some genes with remarkable differences in amino acid identity. All genes with <70% identity between the two variants were found to contain deleted regions when ORFs that could not be expressed were excluded from the comparison. Except in the case of U47, these differences were found in immediate-early/regulatory genes, DR2, DR7, U86/90, U89/90, and U95, which may represent characteristic differences of variants A and B. Also, we have successfully typed 14 different strains belonging to variant A or B by PCR using variant-specific primers; the results suggest that the remarkable differences observed were conserved evolutionarily as variant-specific divergence.

Human herpesvirus 6B genome sequence: coding content and comparison with human herpesvirus 6A

Human herpesvirus 6 variants A and B (HHV-6A and HHV-6B) are closely related viruses that can be readily distinguished by comparison of restriction endonuclease profiles and nucleotide sequences. The viruses are similar with respect to genomic and genetic organization, and their genomes cross-hybridize extensively, but they differ in biological and epidemiologic features. Differences include infectivity of T-cell lines, patterns of reactivity with monoclonal antibodies, and disease associations. Here we report the complete genome sequence of HHV-6B strain Z29 [HHV-6B(Z29)], describe its genetic content, and present an analysis of the relationships between HHV-6A and HHV-6B. As sequenced, the HHV-6B(Z29) genome is 162,114 bp long and is composed of a 144,528-bp unique segment (U) bracketed by 8,793-bp direct repeats (DR). The genomic sequence allows prediction of a total of 119 unique open reading frames (ORFs), 9 of which are present only in HHV-6B. Splicing is predicted in 11 genes, resulting in the 119 ORFs composing 97 unique genes. The overall nucleotide sequence identity between HHV-6A and HHV-6B is 90%. The most divergent regions are DR and the right end of U, spanning ORFs U86 to U100. These regions have 85 and 72% nucleotide sequence identity, respectively. The amino acid sequences of 13 of the 17 ORFs at the right end of U differ by more than 10%, with the notable exception of U94, the adeno-associated virus type 2 rep homolog, which differs by only 2.4%. This region also includes putative cis-acting sequences that are likely to be involved in transcriptional regulation of the major immediate-early locus. The catalog of variant-specific genetic differences resulting from our comparison of the genome sequences adds support to previous data indicating that HHV-6A and HHV-6B are distinct herpesvirus species.

Human herpesvirus 6 open reading frame U83 encodes a functional chemokine

Some viruses including herpesviruses have undergone evolution to benefit viral infection and propagation by pirating and modifying host genes such as chemokine genes. Human herpesvirus 6 (HHV-6), acutely or persistently infects mononuclear cells in vitro. DNA sequence analysis of HHV-6 has revealed that the putative protein encoded by an open reading frame (ORF) of the U83 gene in HHV-6 variant B resembled a human chemokine. We have cloned the U83 gene and analyzed the biological function of this gene. The U83 gene contained an ORF encoding a 113-amino-acid peptide, starting at the first methionine and containing a possible signal peptide and the typical cysteine residues characteristic of the chemokines. Reverse transcription-PCR analysis of mRNA and immunofluorescent-antibody testing of infected cells both indicated that the encoded protein was a late protein. The ORF U83 gene fused to the Fc gene was expressed as a fusion protein in COS-7 cells by transfection, and the fusion protein was purified from the supernatant of transfected cells to test its biological function. The purified protein was capable of inducing transient calcium mobilization in THP-1 cells and of chemotactically activating THP-1 cells. These findings suggested that the U83 protein might play an important role in HHV-6 propagation in vivo by activating and trafficking mononuclear cells to sites of viral replication, thus aiding the development of superbly efficient virus production mechanisms.