ssRNA -ve viruses: segmented vs unsegmented

Graeme Price g.e.price at bham.ac.uk
Tue Nov 7 14:23:02 EST 1995


In article <DHMw99.2tJ at blaze.trentu.ca>, idworkin at ivory.trentu.ca wrote:

>  I am doing some research on  filoviruses and mononegaviridae in
general, I have come across the term segmented vs unsegmented , however my
virology text has n defn for it and have not found any clear meaning for
the term segmented. I am guessing that segmented may be for viruses
without overlapping genes and unsegmented have overlapping genes but if
anyone in virology land can help me by giving me a definition and some
examples I would be very happy.
>  I can be reached here or at IDWORKIN at TRENTU.CA
> 
> thanks in advance
> Ian

Ian,
In the context you are looking at here, segmented means that there are
several different pieces of RNA present within an infectious virion (each
coding for one or more gene products). The classic example of this is
influenza virus which has 8 different segments, each containing a gene
coding for one or two proteins. The filoviruses are non-segmented, meaning
that all the genes are on the same piece of RNA. 

Where you talk about overlapping genes, I guess you mean overlapping
reading frames. Because the genetic code uses 3 bases to determine each
amino acid present in a protein translated from an RNA message, if you had
a sequence which ran (as a very over-simplified example)

ACCGGAUUCA 

This codes for 3 amino acids if you start translation from the first A,
but if you started from the first C instead (this is called a second or
overlapping reading frame), the sequence would now run

CCGGAUUCA ... which codes for 3 completely different amino acids. By using
a second (or even third) reading frame, the same sequence of nucleic acid
can now code for two or three different proteins.

Anyway I hope you get the general idea from this (doubtless if I have made
any major errors the molecular biologists will point it out to me!)

Graeme

-- 
Graeme Price
Microbial Molecular Genetics and Cell Biology Group, 
School of Biological Sciences, Biology West Building,
University of Birmingham,
Edgbaston, Birmingham,
West Midlands, B15 2TT.
United Kingdom.

Tel. (+44) (0)121 414 6555
Fax. (+44) (0)121 414 6557
E-mail g.e.price at bham.ac.uk



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