The nucleotide sequence of an almost-full-length clone of human parvovirus B19 was determined. Whereas the extreme left and right ends of this genomic clone are incomplete, the sequence clearly indicates that the two ends of viral DNA are related by inverted terminal repeats similar to those of the Dependovirus genus. The coding regions are complete in the cloned DNA, and the two large open reading frames which span almost the entire genome are restricted to one strand, as has been found for all other parvoviruses characterized to date. From the DNA sequence we conclude that the organization of the B19 transcription units is similar although not identical to those of other parvoviruses. In particular, we predict that the B19 genome may utilize a fourth promoter to transcribe mRNA encoding the major structural polypeptide, VP2. Analysis of the putative polypeptides confirms that B19 is only distantly related to the other parvoviruses but reveals that there is a small region in the gene probably enicoding the major nonstructural protein of B19, which is closely conserved between all of the parvovirus genomes for which sequence Information is currently available.

No abstract

Nucleotides upstream of the B19 parvovirus P6 promoter affect in vitro transcription in HeLa cell nuclear extracts. Comparison of the relative transcriptional strengths of equimolar mixes of plasmids containing the intact upstream sequence and plasmids containing deletions within these nucleotides identified several regions that affect transcription in vitro. A fragment containing two of five GC-box motifs which correspond to high-affinity SPl-binding sites was shown, by using a gel shift assay, to bind a HeLa cell factor (or factors). DNase I, methylation interference, and methylation protection footprinting demonstrated that the HeLa cell factor(s) bound to one of the two GC-box motifs within this fragment. Mutation of this GC box abolished factor binding and significantly reduces in vitro transcription from the P6 promoter. These results suggest that the B19 parvovirus promoter includes a complex regulatory region containing multiple sequences which affect promoter strength and that the GC-box motif is a major controlling sequence for in vitro transcription.

All mammalian parvovirus genomes characterized to date contain imperfect terminal palindromes ranging in size from 115nt to 240nt. There are two classes of genomes, those which have direct terminal repeats (TR) (MV-2 and B19) and those in which the terminal hairpin sequences are unrelated (MVM, H-1, and BPV). Terminal hairpins for which the complete sequence is known can be arranged into Tor Y-shaped structures, or more generally "stem plus arms" structures (1). Clones of the human B19 parvovirus contain partial terminal repeats due to incomplete synthesis and/or subsequent deletion of the ends when propagated in E. coli strains

No abstract