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
cactus virus) and nearly complete the sequence of the viral RNA genome from
cDNA clones. RNA viruses are known to be heterogenous (quasi-species), so it
was not surprising to see nucleotide sequence variations when sequences are
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.
Let me try to explain it a little better. We have found 16 nucleotide
substitutions in about 1500 nucleotide of overlapping sequences. There are 11
C to T or T to C substitutions and 5 G to A or A to G substitutions. We have
not found any other possible substituions.
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.
Any comments or suggestions are welcome.
Zxiong at arizvm1.ccit.arizona.edu