Molecular biology

VIRION

Non enveloped, icosahedral capsid with a T=25 symmetry. Capsid’s diameter is about 90-120nm.

GENOME

Non segmented, linear double-stranded DNA of 30 kb encoding about 30 proteins. The genome has terminally redundant sequences which have inverted terminal repetitions (ITR). The terminal protein (TP) is covalently attached to each end of the genome.

GENE EXPRESSION

Transcription is nuclear, in two phases; early (replication), late (virion assembly). All genes are transcribed by host RNA pol II except VA gene which is transcribed by RNA pol III. Genes transcribed by RNA pol II give rise to multiple mRNA that are differentiated by alternative splicing and use of different poly(A) sites.

REPLICATION

NUCLEUS

1. Virus attaches to host receptors though the fiber glycoproteins and is endocytosed into vesicles in the host cell.
2. Disruption of the endosome releases the viral capsid in the cytosol.
3. Attachment to nuclear pore complex leading to release of the DNA into the nucleus.
4. Transcription of early genes (E genes), replication of the DNA genome in the nucleus.
5. Transcription of late genes (L genes), mostly encoding for structural proteins.
6. Assembly of new virions in the nucleus.
7. Virions are released by lysis of the cell.

Epidemiology