ijiwaru at wheel.dcn.davis.ca.us wrote, in part:
>High apparent fidelity of
>replication, or the lack of mutations, may indicate a rather strict
>requirement for specific sequences. This could be caused by the virus
>having intricate regulatory requirements, the need to have conserved
>protein function (you wouldn't want to interrupt the polyprotein before
>the full-length has been translated) or structure (certain conformations
>required for proper processing), or the need for conserved nucleic acid
>secondary and/or tertiary structure (as you have already alluded to).
I have also heard it suggested (with regard to flaviviruses) that the requirements of being able to replicate in two disparate hosts (insects and vertebrates) may be a strong selective pressure, one that limits sequence change.
Ulrich Melcher umelcher at bmb-fs1.biochem.okstate.edu
Department of Biochemistry
and Molecular Biology Tel: 405-744-6210
246 NRC FAX: 405-744-7799
Oklahoma State University
Stillwater OK 74078-3035 USA