An infectious parvovirus B19 (B19V) genotype 2 variant was identified as a high-titer contaminant in a human plasma donation. Genome analysis revealed a 138-bp insertion within the p6 promoter. The inserted sequence was represented by an additional 30 bp from the end of the inverted terminal repeat adjacent to a 108-bp element found also, in inverted orientation, at the extreme right end of the unique sequence of the genome. However, despite the profound variations in the promoter region, the pattern of gene expression and DNA replication did not differ between genotype 1 and genotype 2 in permissive erythroid KU812Ep6 cells. Capsid proteins of both genotypes differ in their amino acid sequences. However, equivalent kinetics of virus inactivation at 56°C or pH 4 indicated a comparable physicochemical stability of virus capsids. Sera from six individuals infected by B19V genotype 1 were investigated on cross-neutralization of B19V genotype 2 in vitro. Similar neutralization of both B19V genotypes was observed in sera from three individuals, while the sera from three other individuals showed weaker cross-neutralization for genotype 2. In conclusion, the in vitro replication characteristics and physical stability of B19V capsids are very similar between human parvovirus B19 genotypes 1 and 2, and cross-neutralization indicates a close antigenic relation of genotypes 1 and 2.

Our data show that B19V is much more vulnerable toward low pH conditions than MMV. Together with the previously reported susceptibility of B19V toward wet heat conditions, low pH is the second treatment where erythrovirus B19V is less resistant than viruses from the parvovirus genus.

Most of the Epstein-Barr virus genome in latently infected cells is in a standard nucleosomal structure, but the region encompassing oriP and the Epstein-Barr virus-encoded small RNA (EBER) genes shows a distinctive pattern when digested with micrococcal nuclease. This pattern corresponds to a previously mapped nuclear matrix attachment region. Although the EBER genes are adjacent to oriP, there is only a two-to fourfold effect of oriP on EBER expression. However, sequences containing a consensus ATF site upstream of EBER1 are important for EBER1 expression.The relationship between gene expression, local chromatin structure, and proximity to origins of DNA replication are all of current interest in the study of gene regulation. The EpsteinBarr virus (EBV) chromosome may be a useful system to study these topics, since it is a relatively large circular doublestranded DNA genome (about 172 kb in length) which is maintained in cell nuclei as a multicopy episome (7, 18). The EBV DNA contains about 85 genes, most of which are transcribed by cell RNA polymerase II, but the two EBV-encoded small RNA (EBER) genes are transcribed by RNA polymerase III. Sensitivity of RNA polymerase III transcription to control by proteins conventionally considered to regulate transcription factors for genes transcribed by RNA polymerase II has been studied recently (20). The EBER genes are located immediately adjacent to the oriP plasmid origin of replication, which is required for the maintenance of the EBV episome in human cells. oriP contains two segments of reiterated binding sites for the EBV EBNA1 protein, the family of repeats (FR) and the dyad symmetry element. In addition to its role in plasmid maintenance, the FR portion of oriP also acts as a transcription enhancer and has been shown to increase transcription from the EBV Cp promoter (23) and the promoter for the LMP1 gene (9), both of which are transcribed by RNA polymerase II.The EBERs are the most abundant EBV transcripts in latently infected cells. EBER1 is 167 nucleotides and EBER2 is 172 nucleotides in length. Neither is thought to be translated into protein, and their functions are uncertain (for a review, see reference 4). Although the EBER genes are not essential for EBV infection of human B lymphocytes and establishment of lymphoblastoid cell lines (24), the EBERs are expressed in several types of EBV-associated cancer. Analysis of the cell growth properties of the Akata Burkitt's lymphoma cell line indicated that EBER genes conferred a more-transformed phenotype on clones of Akata cells that lack EBV, converting their growth properties to be more similar to EBV-positive clones of Akata cells (19). EBERs are not expressed to a significant degree in the lytic EBV infection observed in oral hairy leukoplakia (10), and the transcription of the EBER genes has been shown to be reduced when infected cells are induced to the lytic cycle (11). EBER genes are transcribed by RNA polymerase III, and the EBER genes contain internal promoter sequences similar to those in other pol...

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