Molecular biology and clinical associations of Roseoloviruses human herpesvirus 6 and human herpesvirus 7

Human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) are members of the Roseolovirus genus within the Betaherpesvirinae subfamily. HHV-6 and HHV-7 primary infection occurs in early childhood and causes short febrile diseases, sometimes associated with cutaneous rash (exanthem subitum). Both HHV-6 and HHV-7 are highly prevalent in the healthy population, establish latency in macrophages and T-lymphocytes, are frequently shed in saliva of healthy donors, and the pathogenic potential of reactivated virus ranges from asymptomatic infection to severe diseases in transplant recipients. These features have contributed to the notion that HHV-6 and HHV-7 are more or less "harmless" viruses. Consequently, the medical and scientific interest originally prompted by their discovery has been gradually waning. The aim of this review is to provide a short update of the current knowledge on these viruses, and to suggest that the medical importance of Roseoloviruses should not be understimated.     

唾液中人类疱疹病毒7型的分离与培养

目的：了解人群中人类疱疹病毒7型（HHIV－7）的感染情况,并对HHV－7进行分离培养、鉴定。方法：以聚合酶链反应（PCR）检测唾液中的HHV－7,再以巢式PCR及酶切加鉴别;分离其中2例标本中的病毒,以人脐带血单个核细胞（HCBMC）进行培养,再通过DNA序列测定来鉴定培养结果。结果：检测120例唾液标本有97例阳性,PCR阳性结果示186bp处有一荧光带,经ECORI酶切后成为126bp和60bp两条荧光带,巢式PCR结果示94bp处有一荧光谱,HCBMC可用于HHV－7的传代培养,唾液中分离的HHV－7与培养结果所测得的病毒序列一致。与Berneman分离测得的JI株结果相似,结论：人的唾液中HHV－7检出率高,HHV－7可在HCBMC中增殖。     

Induction of G protein-coupled peptide receptor EBI 1 by human herpesvirus 6 and 7 infection in CD4+ T cells.

EBI 1, a putative lymphocyte-specific G protein-coupled peptide receptor, was induced by human herpesvirus 6 or 7 infection in CD4+ T cells, and its expression increased early after infection and reached a plateau at 48 h. The induction of the EBI 1 gene by human herpesvirus 6 or 7 infection was not mediated by soluble factors but by the virus itself. Deduced from comparisons of the amino acid sequences among members of the G protein-coupled receptor superfamily, these findings suggest that EBI 1 may be a member of the leukocyte chemotactic peptide receptor family.     

Identification of human telomeric repeat motifs at the genome termini of human herpesvirus 7: structural analysis and heterogeneity.

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related T-lymphotropic betaherpesviruses which share a common genomic organization and are composed of a single unique component (U) that is bounded by direct repeats (DRL and DRR). In HHV-6, a sequences have been identified at each end of the DR motifs, resulting in the arrangement aDRLa-U-aDRRa. In order to determine whether determine whether HHV-7 contains similar a sequences, we have sequenced the DRL-U and U-DRR junctions of HHV-7 strain JI, together with the DRR.DRL junction from the head-to-tail concatamer that is generated during productive virus infection. In addition, we have sequenced the genomic termini of an independent isolate of HHV-7. As in HHV-6, a (GGGTTA)n motif identical to the human telomeric repeat sequence (TRS) was identified adjacent to, but not at, the genome termini of HHV-7. The left genome terminus and the U-DRR junction contained a homolog of the consensus herpesvirus packaging signal, pac-1, followed by short tandem arrays of TRSs separated by single copies of a second 6-bp repeat. This organization is similar to the arrangement found at U-DRR in HHV-6 but differs from it in that the TRS arrays are considerably shorter in HHV-7. The right genome terminus and the DRL-U junction contained a homolog of the consensus herpesvirus packaging signal, pac-2, followed by longer tandem arrays of TRSs separated by single copies of either a 6-bp or a 14-bp repeat. This arrangement is considerably more complex than the simple tandem array of TRSs that is present at the corresponding genomic location in HHV-6 and corresponds to a site of both inter- and intrastrain heterogeneity in HHV-7. The presence of TRSs in lymphotropic herpesviruses from humans (HHV-6 and HHV-7), horse (equine herpesvirus 2), and birds (Marek's disease virus) is striking and suggests that these sequences may have functional or structural significance.     

Identification of Campylobacter coli isolates from animals and humans by bacterial restriction endonuclease DNA analysis.

Ninety-nine Campylobacter coli isolates were examined by bacterial restriction endonuclease DNA analysis (BRENDA) with HindIII. Isolates from poultry from the same environment had identical patterns, patterns of isolates carried by suckling piglets were generally the same as those of isolates recovered from their dams, and one human patient yielded the same BRENDA type when sampled 6 weeks later. The 14 human isolates examined produced 11 distinct BRENDA types. Forty-three C. coli isolates from pigs were represented by 20 BRENDA types. Ten C. coli isolates from the feces of gulls yielded five different BRENDA types. Thirty-two C. coli isolates from live chickens and processed chicken yielded five different BRENDA types. Three human isolates had identical DNA patterns; two were from brothers living in the same house, and the third was from a human with no apparent relationship to the brothers. Another human isolate was identical to a poultry isolate. None of the pig strains had DNA patterns resembling those of human strains, nor were the DNA patterns like those of any strains recovered from poultry or gulls. Four C. coli isolates were subcultured onto agar 23 times over a period of 45 days, and their BRENDA patterns were preserved. BRENDA shows great promise for use in epidemiological studies of C. coli.     

Human herpesvirus 6B origin: sequence diversity, requirement for two binding sites for origin-binding protein, and enhanced replication from origin multimers.

A previously identified human herpesvirus 6B (HHV-6B) origin of DNA replication contains two binding sites for the origin-binding protein (OBPH6B). We have investigated the functional significance of these sites by determining the replication efficiencies of mutated origin sequences, using a transient replication assay. The results indicate that both sites are required for DNA replication. In addition, we have tested the functional consequences of linear sequence amplifications in the origin. The data show that tandemized origin elements are more efficiently replicated than single-copy origins. Finally, we have determined the extent of interstrain origin sequence variation that exists among HHV-6 isolates by cloning, sequencing, and analyzing origins from a number of virus isolates, including examples of both HHV-6A and HHV-6B.     

Identification of Campylobacter coli isolates from animals and humans by bacterial restriction endonuclease DNA analysis

Ninety-nine Campylobacter coli isolates were examined by bacterial restriction endonuclease DNA analysis (BRENDA) with HindIII. Isolates from poultry from the same environment had identical patterns, patterns of isolates carried by suckling piglets were generally the same as those of isolates recovered from their dams, and one human patient yielded the same BRENDA type when sampled 6 weeks later. The 14 human isolates examined produced 11 distinct BRENDA types. Forty-three C. coli isolates from pigs were represented by 20 BRENDA types. Ten C. coli isolates from the feces of gulls yielded five different BRENDA types. Thirty-two C. coli isolates from live chickens and processed chicken yielded five different BRENDA types. Three human isolates had identical DNA patterns; two were from brothers living in the same house, and the third was from a human with no apparent relationship to the brothers. Another human isolate was identical to a poultry isolate. None of the pig strains had DNA patterns resembling those of human strains, nor were the DNA patterns like those of any strains recovered from poultry or gulls. Four C. coli isolates were subcultured onto agar 23 times over a period of 45 days, and their BRENDA patterns were preserved. BRENDA shows great promise for use in epidemiological studies of C. coli.     

Species specificity of macaque rhadinovirus glycoprotein B sequences

All members of the Herpesviridae family contain sequences for a highly conserved glycoprotein B (gB) gene. We investigated the phylogenetic relationships of gB sequences from eight independent rhadinovirus isolates obtained from three species: rhesus (Macaca mulatta), cynomologus (Macaca fasicularis), and pig-tailed (Macaca nemestrina) macaques. Samples were derived from monkeys housed at four separate facilities. Analysis of these eight independent gB sequences revealed five regions of heterogeneity within the 823- to 829-amino-acid polypeptides: residues 1 to 65, 120 to 185, 255 to 300, 352 to 393, and 412 to 457. The remaining regions of gB were highly conserved among the different macaque isolates. Overall divergence among these gene sequences ranged from 0.1 to 7.2% at the amino acid level. Phylogenetic trees constructed with our macaque rhadinovirus gB sequences and those derived from additional subfamilies or genera (alpha, beta, gamma-1, and gamma-2) revealed that the macaque gB sequences branched with other gamma-2 herpesvirus gB sequences and that within the gamma-2 genera, the macaque gB sequences clustered as a distinct branch. The eight macaque rhadinovirus gB sequences were all approximately equidistant from Kaposi sarcoma-associated herpesvirus (KSHV) gB sequences and had a shorter evolutionary distance to KSHV gB sequences than to any other herpesvirus, including the gamma-2 herpesvirus saimiri (HVS) of New World squirrel monkeys. The macaque gB sequences did not cluster according to the facility of origin, but did cluster according to the species of origin, displaying less intraspecies divergence (0.1 to 2.9%) than interspecies divergence (3.3 to 7.2%). These results demonstrate a close relatedness of rhadinovirus isolates from different macaque species.     

Detection of human herpesvirus 6 and 7 DNA in saliva from healthy adults from Rio de Janeiro, Brazil

In this study, we aimed to evaluate virus shedding in the saliva of healthy adults from the metropolitan region of the city of Rio de Janeiro, Brazil, in order to verify the prevalence of both human herpesviruses 6 and 7 (HHV-6, HHV-7). The studied group comprised 182 healthy individuals at Pedro Ernesto University Hospital, who were being seen for annual odontologic revisions. Saliva specimens were subjected to a multiplex polymerase chain reaction (PCR) to detect the presence of HHV-6A, HHV-6B and HHV-7. The total Roseolovirus DNA prevalence was 22.4%. The PCR detected a HHV-6 prevalence of 9.8%, with HHV-6A detected in 7.1% of the samples and HHV-6B in 2.7%. HHV-7 DNA was revealed in 12.6% of the studied cases. Multiple infections caused by HHV-6A and 7 were found in 2.1% of the samples. No statistical differences were observed regarding age, but for HHV-7 infection, an upward trend was observed in female patients. Compared to studies from other countries, low prevalence rates of herpesvirus DNA were detected in saliva from the healthy individuals in our sample. PCR methodology thus proved to be a useful tool for Roseolovirus detection and it is important to consider possible geographic and populations differences that could explain the comparatively low prevalence rates described here.     

Characterization of Escherichia coli O157:H7 from downer and healthy dairy cattle in the upper Midwest region of the United States

While cattle in general have been identified as a reservoir of Escherichia coli O157:H7, there are limited data regarding the prevalence and clonality of this pathogen in downer dairy cattle and the potential impact to human health that may occur following consumption of meat derived from downer dairy cattle. In the present study, conducted at two slaughter facilities in Wisconsin between May and October of 2001, we established a higher prevalence of E. coli O157:H7 in fecal and/or tissue samples obtained aseptically from intact colons of downer dairy cattle (10 of 203, 4.9%) than in those from healthy dairy cattle (3 of 201, 1.5%). Analyses of 57 isolates, representing these 13 positive samples (one to five isolates per sample), by pulsed-field gel electrophoresis, revealed 13 distinct XbaI restriction endonuclease digestion profiles (REDP). Typically, isolates from different animals displayed distinct REDP and isolates from the same fecal or colon sample displayed indistinguishable REDP. However, in one sample, two different, but highly related, REDP were displayed by the isolates recovered. Antimicrobial susceptibility testing indicated that 10 of the 57 isolates, recovered from 2 (1 downer and 1 healthy animal) of the 13 positive samples, were resistant to at least 1 of 18 antimicrobials tested. However, there was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle, and not all isolates with the same REDP displayed the same antimicrobial susceptibility profile. Lastly, it was not possible to distinguish between isolates recovered from downer and healthy cattle based on their XbaI REDP or antimicrobial susceptibility. These results indicate that downer cattle had a 3.3-fold-higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study.     

贵州省25株狂犬病病毒核蛋白基因序列分析

分析贵州省25株狂犬病病毒的核蛋白基因(N基因)序列,探讨贵州省狂犬病流行特征与狂犬病病毒变异情况。以RT-nested PCR检测来自贵州省2005年至2010年不同地区的病人脑组织、病人唾液以及犬脑组织标本狂犬病病毒RNA,经测序与拼接后得到25条N基因全长序列,采用生物信息学软件对N基因序列进行分析。25株狂犬病病毒核蛋白在核苷酸及氨基酸水平上彼此的同源性分别为89.3%～100%和98.%～100%;与国内其他省已发表基因1型狂犬病病毒核苷酸和氨基酸序列同源性分别为88%～99.1%和88%～99.7%,与已知的基因1型狂犬病病毒比较,25株病毒核蛋白氨基酸序列发生了若干位点的取代。进化树分析显示,同一地区内与相邻地区,以及同一时间段与相邻时间段内狂犬病病毒N基因进化亲缘关系相近。25株贵州省狂犬病病毒流行毒株均属基因1型,其核蛋白在基因的核苷酸及推导的氨基酸水平上均有变异,且这些变异具有地域和时间分布特性。     

Molecular analysis of the microbial diversity present in the colonic wall, colonic lumen, and cecal lumen of a pig

Random clones of 16S ribosomal DNA gene sequences were isolated after PCR amplification with eubacterial primers from total genomic DNA recovered from samples of the colonic lumen, colonic wall, and cecal lumen from a pig. Sequences were also obtained for cultures isolated anaerobically from the same colonic-wall sample. Phylogenetic analysis showed that many sequences were related to those of Lactobacillus or Streptococcus spp. or fell into clusters IX, XIVa, and XI of gram-positive bacteria. In addition, 59% of randomly cloned sequences showed less than 95% similarity to database entries or sequences from cultivated organisms. Cultivation bias is also suggested by the fact that the majority of isolates (54%) recovered from the colon wall by culturing were related to Lactobacillus and Streptococcus, whereas this group accounted for only one-third of the sequence variation for the same sample from random cloning. The remaining cultured isolates were mainly Selenomonas related. A higher proportion of Lactobacillus reuteri-related sequences than of Lactobacillus acidophilus- and Lactobacillus amylovorus-related sequences were present in the colonic-wall sample. Since the majority of bacterial ribosomal sequences recovered from the colon wall are less than 95% related to known organisms, the roles of many of the predominant wall-associated bacteria remain to be defined.     

细脚拟青霉田间分离菌株间的异核现象

本文报道细脚拟青霉(paecilomyces tenuipes)不同田间分离菌株单孢子后代间的异核现象。用来自荣园、菜地、水稻田三种生境的四个菌株(803、2801、1401和3101)的单孢子培养后代,在加有酵母膏和麦芽糖的改良萨氏培养基上进行配接实验,仅在803与1401两菌株间能形成异核体,其频率为13.5%。在配接实验中两亲和菌落交界处长出白色致密的菌丝簇组成的实线可推测为异核体。从来自菌丝簇组线的每个单菌丝尖端培养物中分离出30个以上的单孢子,井分别移接到 PDA 平板上。将来源于单孢子的菌落与两亲本菌落进行比较,有三个单菌丝尖端培养物(C_3、B_3、F_3)重现了两亲本类型或出现了新的菌落类型,从而异核现象得到证实。     

Oral cavity as natural reservoir for intestinal lactobacilli

Ecological studies indicate that most Lactobacillus species found in the human gastrointestinal tract are likely to be transient (allochthonous), originating from either the oral cavity or food. In order to investigate if oral lactobacilli constitute a part of the faecal Lactobacillus biota, the Lactobacillus biota of saliva and faeces of three human subjects were investigated and compared at two time-points in a 3-months interval. Bacteriological culture, performed by incubation under standard (37 degrees C, anaerobic) and alternative (30 degrees C, microaerobic) conditions, as well as PCR-DGGE with group-specific primers were used to characterize the predominant lactobacilli. Cell counts varied among the subjects and over time, reaching up to 10(7)CFU/ml in saliva and 5 x 10(6)CFU/g in faecal samples. The species composition of the Lactobacillus biota of human saliva and faeces was found to be subject-specific and fluctuated to some degree, but the species Lactobacillus gasseri, Lactobacillus paracasei, Lactobacillus rhamnosus and Lactobacillus vaginalis were detected at both time-points in saliva and faecal samples of individual subjects. RAPD-PCR analysis indicated that several strains of these species were present both in the oral cavity and in the faecal samples of the same subject. Oral isolates of the species L. gasseri and L. vaginalis showing identical RAPD types were found to persist over time, suggesting that these species are autochthonous to the oral cavity. Our results together with recent published data give strong evidence that some lactobacilli found in human faeces are allochthonous to the intestine and originate from the oral cavity.     

Characterization of Escherichia coli O157:H7 from Downer and Healthy Dairy Cattle in the Upper Midwest Region of the United States

While cattle in general have been identified as a reservoir of Escherichia coli O157:H7, there are limited data regarding the prevalence and clonality of this pathogen in downer dairy cattle and the potential impact to human health that may occur following consumption of meat derived from downer dairy cattle. In the present study, conducted at two slaughter facilities in Wisconsin between May and October of 2001, we established a higher prevalence of E. coli O157:H7 in fecal and/or tissue samples obtained aseptically from intact colons of downer dairy cattle (10 of 203, 4.9%) than in those from healthy dairy cattle (3 of 201, 1.5%). Analyses of 57 isolates, representing these 13 positive samples (one to five isolates per sample), by pulsed-field gel electrophoresis, revealed 13 distinct XbaI restriction endonuclease digestion profiles (REDP). Typically, isolates from different animals displayed distinct REDP and isolates from the same fecal or colon sample displayed indistinguishable REDP. However, in one sample, two different, but highly related, REDP were displayed by the isolates recovered. Antimicrobial susceptibility testing indicated that 10 of the 57 isolates, recovered from 2 (1 downer and 1 healthy animal) of the 13 positive samples, were resistant to at least 1 of 18 antimicrobials tested. However, there was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle, and not all isolates with the same REDP displayed the same antimicrobial susceptibility profile. Lastly, it was not possible to distinguish between isolates recovered from downer and healthy cattle based on their XbaI REDP or antimicrobial susceptibility. These results indicate that downer cattle had a 3.3-fold-higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study.     

Molecular characterization of Irish E. coli O157:H7 isolates of human, bovine, ovine and porcine origin

Aims:  To determine the degree of relatedness between isolates of Escherichia coli O157:H7 of human, bovine, ovine and porcine origin.
Methods and Results:  Escherichia coli O157:H7 isolates were compared using (i) PFGE Xba I patterns, (ii) PCR profiles of virulence genes and (iii) the DNA sequences of genes reported to play a role in pathogenicity. The 77 E. coli O157:H7 isolates demonstrated 49 different PFGE patterns of which, eight were common to multiple isolates, and the remaining 41 were distinct. Isolates of different origin did not correlate, except for one cluster consisting of two human and two beef isolates. The majority of animal isolates had the same PCR profiles of virulence genes as those isolated from clinical patients. Single nucleotide polymorphisms (SNPs) were identified in the sequence of a 255-bp region of the vtx2 subunit A gene.
Conclusions:  Six SNPs were detected in the vtx2 A gene, defining four different haplotypes. One nonsynonymous substitution encoded for an amino acid change from glutamic to aspartic acid.
Significance and Impact of the Study:  Results indicate that although E. coli O157:H7 isolates of differing origin were distinct by PFGE, the DNA sequences of the main virulence genes associated with human clinical illness were conserved.     

Characterization of Glycoprotein H and L of Human Herpesvirus 7

The genes encoding the glycoproteins H (gH) and L (gL) of human herpesvirus 7 (HHV-7) have been identified. The gH open reading frame (ORF) was 2,070 base pairs in length and encoded a predicted 690 amino-acid protein. The gH contained characteristics of a transmembrane glycoprotein including 10 consensus N-linked glycosylation sites, 12 cysteine residues, a potential amino-terminal signal sequence and a predicted transmembrane segment located near the carboxyl terminus. The gL ORF was 738 base pairs in length and encoded a predicted 246 amino-acid protein. Four possible N-glycosylation sites and 6 cysteine residues existed within gL. The predicted amino-acid sequences of the HHV-7 gH and human herpesvirus 6 variant A (HHV-6A) gH gene products exhibited 23.6% identity to each other, and those of the gL gene products had 26.0% identity. Upon in vitro translation of the gL gene, the addition of microsomal membranes resulted in two modified products with molecular weights of 32 kDa and 35 kDa from the unmodified initial translation product of 26 kDa. An amino-terminal portion of gH and the full length of gL were expressed as glutathione S-transferase fusion proteins, and these proteins were used to raise immune sera in mice. Lysates of cells infected with HHV-7 were subjected to immunoprecipitation analysis. Approximate molecular weights of 33, 37, 80 and 90 kDa polypeptides were immunoprecipitated with antibodies against the gH protein. Antibodies against the gL protein polypeptides with the same molecular weights were also precipitated, and were observed with the antibodies against the gH protein. These results suggest that HHV-7 gH and gL may form a heterodimeric complex with each other in HHV-7 infected cells, as has been reported for other herpesviruses.     

Expanding distribution of human serotype G6 rotaviruses in Australia

Serotype G6 rotaviruses are common pathogens of cattle but are rarely found in humans. In Australia, human G6 isolates have previously been detected in two major southern population centres. A new isolate, ASG6.02, was detected in central Australia (Alice Springs) in 1997. Comparison of the deduced amino acid sequence of the major neutralizing antigen, VP7, indicated that ASG6.02 was related to human G6 viruses isolated from children in Italy and Australia. Phylogenetic analysis supported the close relationship between ASG6.02 and other Australian isolates and indicated that G6 VP7 sequences generally clustered according to the species of origin (human, bovine or porcine). The VP4 type of ASG6.02 was determined as P-type [14], in common with other isolates from Australia and Italy. The detection of ASG6.02 indicates that the distribution of this serotype is increasing in this country and may have implications for successful vaccine development.     

Specificity analysis of human CD4+ T-cell clones directed against human herpesvirus 6 (HHV-6), HHV-7, and human cytomegalovirus.

In order to clarify antigenic variations among various isolates of human herpesvirus 6 (HHV-6) and cross-reactivity among HHV-6, HHV-7, and human cytomegalovirus (HCMV) in the T-cell immune response, the antigenic specificity of the proliferative response mediated by 232 CD4+ human T-cell clones directed against HHV-6, HHV-7, or HCMV was examined. The results obtained were as follows. (i) Although the majority of T-cell clones directed against HHV-6 proliferated in response to stimulation with all strains of HHV-6 used (U1102, Z29, SF, and HST), 7% (8 of 122) of the T-cell clones showed distinct patterns of proliferative response against strain U1102 (group A) and other strains of HHV-6 (group B). (ii) Of 99 T-cell clones, 71 showed a distinct proliferative response to HHV-6 and HHV-7, whereas 28 proliferated in response to stimulation with both HHV-6 and HHV-7. (iii) A small number of T-cell clones (9 of 232) showed cross-reactivity against HHV-6 and HCMV, and 2 of the 232 clones were reactive with HCMV as well as with HHV-6 and HHV-7. (iv) The specificity of gamma interferon production by T-cell clones following the stimulation with virus antigen was identical to that of their proliferative response. These data thus indicate the presence of antigenic variations among isolates of HHV-6 and also epitopes common to HHV-6 and HHV-7 and to HHV-6, HHV-7, and HCMV which are recognized by CD4+ T cells.     

Structure and heterogeneity of the a sequences of human herpesvirus 6 strain variants U1102 and Z29 and identification of human telomeric repeat sequences at the genomic termini.

The unit-length genome of human herpesvirus 6 (HHV-6) consists of a single unique component (U) bounded by direct repeats DRL and DRR and forms head-to-tail concatemers during productive infection. cis-elements which mediate cleavage and packaging of progeny virions (a sequences) are found at the termini of all herpesvirus genomes. In HHV-6, DRL and DRR are identical and a sequences may therefore also occur at the U-DR junctions to give the arrangement aDRLa-U-aDRRa. We have sequenced the genomic termini, the U-DRR junction, and the DRR.DRL junction of HHV-6 strain variants U1102 and Z29. A (GGGTTA)n motif identical to the human telomeric repeat sequence (TRS) was found adjacent to, but did not form, the termini of both strain variants. The DRL terminus and U-DRR junction contained sequences closely related to that of the well-conserved herpesvirus packaging signal Cn-Gn-Nn-Gn (pac-1), followed by tandem arrays of TRSs separated by single copies of a hexanucleotide repeat. HHV-6 strain U1102 contained repeat sequences not found in HHV-6 Z29. In contrast, the DRR terminus of both variants contained a simple tandem array of TRSs and a close homolog of a herpesvirus pac-2 signal (GCn-Tn-GCn). The DRR.DRL junction was formed by simple head-to-tail linkage of the termini, yielding an intact cleavage signal, pac-2.x.pac-1, where x is the putative cleavage site. The left end of DR was the site of intrastrain size heterogeneity which mapped to the putative a sequences. These findings suggest that TRSs form part of the a sequence of HHV-6 and that the arrangement of a sequences in the genome can be represented as aDRLa-U-a-DRRa.