Reproductive Cycle in a Host Cell

Each different picornaviridae virus will use its own different cellular receptors.

• A picornavirus virion attaches to a host cell.


• Uncoating occurs, and the virus' RNA is released into the cytoplasm of the host cell through a membrane channel.
  

• The host cell's transcription processes are shut off to a degree that varies with different picornaviruses, while the IRES helps to make sure the virus' transcription is left untouched.


• Replication occurs in cytoplasm. In vitro transcription studies have suggested 2 possible models by which genome replication might occur:

• RNA is packaged into preformed capsids.


• The viruses are released when cell lysis occurs.
  
  

picture extracted: http://www.microbiologybytes.com/virology/Picornaviruses.html http://gsbs.utmb.edu/microbook/ch042.htm

References:
http://www.microbiologybytes.com/virology/Picornaviruses.html http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.052.htm#quickIDX2 http://www.stanford.edu/group/virus/picorna/2004flynn/Picornaviridae2.htm

Genome Structure and Virion Structure

Genome Structure

• Its genome consist of a single molecule of linear, positive, single strand RNA and it not non-segmented.


• The complete genome is 7000-8500 nucleotides long.

Virion Structure of a Picornaviridae

• Picornavirus virions consist of a non-enveloped, icosahedrally symmetric capsid.


• The capsid consists of 12 capsomers and has a diameter of 27-30 nm,


• One of the smallest of all viruses.


• Genome is tightly packed into the capsid.


• The capsid has four unique proteins which are VP1, 2, 3, and 4.

Virion

Picture extracted: http://www.expasy.ch/viralzone/all_by_protein/33.html

Picornarviridae

It is the oldest viruses which found in ancient Egypt at 1400 B.C. Picornaviruses are also among the most diverse viruses, with over 200 serotypes causing infections such as Polio, Hepatitis A, and the common cold. Foot-and-Mouth Disease Virus (genus: Apthovirus), which causes infections in livestock, was one of the first viruses to be recognized; it was discovered by Loeffler and Frosch in 1898.

• Picornaviruses contain positive sense, single-stranded RNA that is approximately 7-8 kilobases long.


• The viral RNA is infectious and replication takes place in the cytoplasm.


• The virus has an IRES (Internal Ribosomal Entry Site) which distinguishes it from many other RNA viruses.


• The virus is naked with an icosahedral capsid.


• The capsid is one of the smallest of all viruses with a diameter of only 27-30nm.


• Translation and cleavage of viral polypeptides produces eleven distinct proteins.

Picture extracted: http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/dkpolio.html