Questions: G to A and C to T substitutions, is this a rule ?

bhjelle at bhjelle at
Mon Apr 11 18:56:18 EST 1994

In article <zxiong.49.000DC98F at>,
Zhongguo Xiong <zxiong at> wrote:
>Dear Colleagues:
>Being not familiar with molecular evolution. I have been troubled with some of 
>my data in RNA virus sequence. We are working on a small RNA virus (Saguaro 

>obtained from different clones. What was surprising was a consistent rule of 
>sequence variaions. G is always subsituted with a A, or vice versa. C is 
>always substituted with a T, or vice versa. But there is never a G to (C, T) 
>change or vice versa.
>Is there a theory describing the rule  of nucleotide substitution during 
>evolution? I feel very ignorant and hope someone can give me a pointer to how 
>to explain my observation.
We certainly see this in hantavirus. Also
with transitions favored greatly over
transversions. There is a computer program
called MacClade that enables you to formally
evaluate this bias in character state
changes, and use the data to prepared
"weighted" phylogenetic trees for studies
of viral evolution. Write clade at
This is also seen with HIV. I don't know
*why* viruses do this. It seems to be 
somewhat virus-specific.


More information about the Virology mailing list