I wanted to briefly comment on a point in this critique of Behe on HIV that I think was overlooked.
The part I wanted to comment on was this:
The feature both Vpus have in common, CD4 degradation, is carried out in completely different ways. HIV-1 Vpu requires two casein kinase II sites. You could almost call it irreducibly complex "“ if you dont have both CKII sites, CD4 isn't degraded. Yet some SIVcpz Vpus have only one CKII site, and instead utilize a simple string of negatively charged amino acids in place of the second site.
Update: Behe responds andÂ that mean girlsÂ reference is hilarious
First, it's not really surprising that some SIVcpz Vpus have only one CK II site, and have a string of negatively charged amino acids in place of the second site. CK-II site phosphorylation also results in negative charge. So it is probably a case of similarly imparted structual conformation.
I found it interesting though, that virtually all HIV-1 sequences have both serines, even though they undergo so much variation during replication. The reason why may actually be that changing from a serine, to , say aspartate, requires at least two nucleotide substitutions, thus resulting in a rugged fitness landscape where a possible tranversion would result in a poor replicator. It's got to climb up a peak in order to mutate again to aspartate. So here we get a better understanding of Behe's thinking regarding "the edge of evolution".