1. Characteristics of Eukaryotic Viruses

• •  Obligate intracellular parasites

•  Infect and reproduce only within the living eukaryotic cells

•  Viruses contain single or double stranded DNA or RNA as their genomes (Fig. 1)

•  ssRNA able to function as mRNA is referred to as positive (+) sense or plus strand RNA and if it is the equivalent to antisense RNA it said to be as minus strand or negative (-) sense RNA

•  In certain cases, the genome encodes mRNAs which are of either sense

•  Processes that are found both in eukaryotes and their viruses- Glycosylation, RNA processing and protein modification (proteolytic cleavage)

Fig. 11. General structure of enveloped Eukaryotic Virus

2. Structure of Eukaryotic viruses

• •  The viral genome is enclosed by a protein coat known as capsid.

•  Capsid composed of protein subunits known as capsomeres

•  The nucleic acid genome along with the protective protein coat is called the nucleocapsid.

•  Nucleocapsid can be of following symmetry:

•  Icosahedral,

•  Helical or

•  Enveloped symmetry

•  Majority of viruses have helical or icosahedral symmetry