Retroviruses and Hepatitis B Virus

Rous Sarcoma Virus

Hepatitis B Virus

HBV Genome

Genome Organization

4 classes of mRNA in green :0.9kb, 2.1kb, 2.4kb, 3.5kb

Pregenome RNA blue

Outline of Genome Replication• The pregenome RNA acts as template for DNA synthesis. • Initially a 4-nucleotide (−) DNA is synthesized then it is transferred to a

complementary sequence in DR1 near the 3 end of the pregenome.• DNA synthesis continues to the 5 end of the pregenome template. The RNase

H activity of the P protein degrades the pregenome RNA from the RNADNA duplex.

• All the RNA is removed except for a remnant of 15–18 bases including the cap. The –OH group at the 3 end of the RNA remnant acts as the primer for the synthesis of (+) DNA.

• During (+) DNA synthesis a nucleocapsid can either migrate to the nucleus to increase the pool of cccDNA or it can undergo a maturation event that enables it to bud through a membrane containing virus envelope proteins

• DNA synthesis ceases on budding, as the nucleocapsid is cut off from the pool of nucleotides in the cytoplasm.

• This explains why the (+) DNA in the virion is incomplete?

Epsilon elements

Steps in RT Pathway