IDENTIFICATION OF A NEW HEPATITIS-B-VIRUS (HBV) GENOTYPE FROM BRAZIL THAT EXPRESSES HBV SURFACE-ANTIGEN SUBTYPE ADW4

The complete genome of a hepatitis B virus (HBV) from Brazil that expr essed the subtype adw4 of HBV surface antigen (HBsAg) was cloned and s equenced. The genome, termed w4B, consists of 3215 bp. The overall gen etic organization of typical hepadnaviruses with four open reading fra mes including the preC region was found to be conserved. When comparin g the w4B sequence with 19 complete HBV genomes it was, however, found to be more divergent (15%) than any other HBV sequence thus far repor ted. Until now, no more than 11% divergence has been reported. Distinc t from the five known HBV genotypes A to E, w4B made up a new, sixth g enotype. The importance of the conserved third start codon in the HBV X gene became apparent in isolate w4B. By mutation, this ATG was out o f frame, and by what appears to have been a linked mutation, a new sta rt site two codons downstream was re-established. The significance of several other mutations is discussed.