FIG 1.

B19V transcription map. (A) B19V packages a linear ssDNA genome of either positive or negative polarity. The ssDNA genome of B19V is shown in negative polarity. Two ITRs (nt 1 to 383 and nt 5214 to 5596) are diagrammed at two ends of the genome with unpaired or mismatched bases in the palindromes represented by “bulges” or “bubbles,” respectively. (B) Schematic diagram of the duplex replicative form (RF) of the B19V genome. It is capable of expressing viral genes, replicating, and producing progeny virions. The P6 promoter, the RNA initiation site, splice donor sites (D1 and D2), splice acceptor sites (A1-1, A1-2, A2-1, and A2-2), and proximal/distal polyadenylation sites [(pA)p/(pA)d] are indicated, along with the nine major mRNAs (R1 to R9) that are polyadenylated at nt 2840 of the major (pA)p site and three minor mRNAs (R1′ to R3′) that are polyadenylated at nt 3141 of the minor (pA)p site. The numbering of nucleotides is according to the numbering for the B19V J35 isolate (GenBank accession no. AY386330). Proteins encoded by each mRNA are shown on the right with detected molecular masses in kilodaltons. The ITRs and the NS1- and VP1-encoding regions are not to scale. The coding capabilities of R3 and R3′ mRNAs are unknown. The size of each mRNA is shown in nucleotides without inclusion of the poly(A) tail. Different ORFs are depicted in different-colored boxes.