- Volume 83, Issue 8, 2002

In this report a naturally occurring hypervariable region within the genome of different Cryptophlebia leucotreta granulovirus genotypes is characterized. The region consists of a stretch of direct repeats, short palindromes and an unusual AT-rich region. Although the organization of these repeat sequences is unique to baculoviruses, it has the structural features of a ‘non-hr’ origin of DNA replication (ori). Restriction analysis and Southern hybridization revealed that this region is expanded during virus replication. Sequence comparison of different isolated genotypes indicated that the expansion is caused by concatenation of short repeats within the region or by concatenation of the complete region. These findings indicate that the expansion of non-hr origin-like regions is not restricted to defective-interfering particles, as was found previously for baculoviruses propagated in cell culture. Moreover, it appears that non-hr complexity contributes to the natural heterogeneity and genetic plasticity of baculovirus genomes. Also, circumstantial evidence is discussed that hr oris might have developed from internal rearrangement and multiplication of a non-hr ori during baculovirus evolution.

Polydnaviruses are unique viruses: they are essential for successful parasitism by tens of thousands of species of parasitoid wasps. These viruses are obligatorily associated with the wasps and are injected into the host during oviposition. Molecular analyses have shown that each virus sequence in the segmented polydnavirus genome is present in the wasp DNA in two forms: a circular form found in the virus particles and an integrated form found in the wasp chromosomes. Recent studies performed on polydnaviruses from braconid wasps suggested that the circular forms were excised from the chromosome. The different forms of the EP1 circle of Cotesia congregata polydnavirus during the pupal–adult development of the parasitoid wasp were analysed. Unexpectedly, an off-size fragment formerly used to diagnose the integration of the EP1 sequence into wasp genomic DNA was found to be amplified in female wasps undergoing virus replication. The EP1 sequence is amplified within a larger molecule comprising at least two virus segments. The amplified molecule is different from the EP1 chromosomally integrated form and is not encapsidated into virus particles. These findings shed light on a new step towards EP1 circle production: the amplification of virus sequences preceding individual circle excision.

The E1 region of adenovirus (Ad) type 5 is capable of transforming cells. According to current concepts, the Ad E1B 55 kDa (E1B 55K) protein enables transformed cells to grow by constantly binding and inactivating the p53 tumour suppressor protein. To test this model, the transcriptional activity of p53 was determined in Ad E1-transformed cells. Surprisingly, it was found that a p53-responsive promoter is highly active in Ad E1-transformed cells and further activated only 3- to 4-fold (compared to 200-fold in p53 −/− cells) by exogenously expressed p53 or p53mt24–28, a p53 mutant that is transcriptionally active but unable to bind the E1B 55K. On the other hand, the transient overexpression of E1B 55K led to a strong downregulation of a p53-responsive promoter relative to its baseline activity in Ad E1-transformed cells but not in p53 −/− cells. COS-7 cells, transformed by simian virus 40 (SV40), also showed constitutive p53 activity, whereas HeLa cells, transformed with oncogenic human papillomavirus, did not. Upon stable transfection, Ad E1-transformed cells but not p53 −/− cells gave rise to colonies that expressed exogenous p53 or p53mt24–28 but, nonetheless, grew at near-wild-type rates. It is proposed that E1B 55K or the SV40 tumour antigen are saturated by the p53 protein, which accumulates in virus-transformed cells, leaving a proportion of active p53 molecules. The transformation of cells by the Ad E1 genes confers permissiveness for active p53, conceivably by inactivating the relevant products of p53 target genes that would otherwise prevent cell growth. Thus, Ad-transformed cells contain and tolerate active p53.

The complete genomes were sequenced for ten hepatitis B virus (HBV) strains. Two of them, from Spain and Sweden, were most similar to genotype D, although encoding d specificity. Five of them were from Central America and belonged to genotype F. Two strains from Nicaragua and one from Los Angeles, USA, showed divergences of 3·1–4·1% within the small S gene from genotype F strains and were recognized previously as a divergent clade within genotype F. The complete genomes of the two genotype D strains were found to differ from published genotype D strains by 2·8–4·6%. Their S genes encoded Lys122, Thr127 and Lys160, corresponding to the putative new subtype adw3 within this genotype, previously known to specify ayw2, ayw3 or, rarely, ayw4. The complete genomes of the three divergent strains diverged by 0·8–2·5% from each other, 7·2–10·2% from genotype F strains and 13·2–15·7% from other HBV strains. Since pairwise comparisons of 82 complete HBV genomes of intratypic and intertypic divergences ranged from 0·1 to 7·4% and 6·8 to 17·1%, respectively, the three sequenced strains should represent a new HBV genotype, for which the designation H is proposed. In the polymerase region, the three strains had 16 unique conserved amino acid residues not present in genotype F strains. So far, genotype H has been encountered in Nicaragua, Mexico and California. Phylogenetic analysis of the complete genomes and subgenomes of the three strains showed them clustering with genotype F but forming a separate branch supported by 100% bootstrap. Being most similar to genotype F, known to be an Amerindian genotype, genotype H has most likely split off from genotype F within the New World.

Rodent parvoviruses have been documented to interfere with both in vivo and in vitro research. In this study, three rat parvoviruses distinct from previously characterized rodent parvoviruses were identified from naturally infected rats obtained from four discrete sources. These three newly recognized parvoviruses were designated rat minute virus (RMV)-1a, -1b and -1c. In this study, the genomic nucleotide sequence and the predicted amino acid sequences of proteins for each of the three RMV-1 variants and Kilham rat virus (KRV) were determined and compared with previously characterized rodent parvoviruses. The three RMV-1 variants were shown to be closely related to each other, to be distinct from but closely related to KRV and H-1 virus, and to be significantly different from the previously identified rat parvovirus isolate, RPV-1a.