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Excerpt
Many mutations in the CCR5 coding region have been reported; prominent among them is the 32 base pair (bp) deletion corresponding to the second extracellular region, which affords nearly total protection against HIV-1 infection. This mutation is quite common among Caucasian people of European heritage but is extremely rare in Asian countries [2]. It is for this reason that the CCR5 gene has become an attractive target as an antiviral approach [3]. Interestingly, the parallel evolution of null alleles of CCR5 have been reported in humans and the sooty mangabey [4].
HIV does not normally cause disease in non-human primates, although infection and active replication have been demonstrated by many investigators. Similarly, non-human primates (African green monkeys and sooty mangabeys) support active replication of SIV but do not develop symptoms of the disease typical of a retrovirus (for review see Edinger et al. [5]). A satisfactory explanation of these observations has been difficult to find, but given the importance of chemokines and chemokine receptors in modulating the disease in both non-human primates and humans, it is likely that they may be playing a role in modulating the disease. A homozygous G–A transition (nucleotide position 801 with respect to the ATG initiation codion) in the 3' untranslated region of the gene for stromal cell derived factor, SDF-1, was shown to be associated with the delayed progression of the disease in humans [6]. The reasons for this delay are currently not known, but it may be caused by upregulation of the expression of SDF-1, which could block the CXCR4 receptors (HIV-1 co-receptor for X4 viruses).
In the present study, we sought to characterize the 3' untranslated regions of the SDF-1 genes of four different species of monkeys (rhesus, marmoset, baboon and bonnet). The forward and backward primers for genotyping were the same for humans and monkeys, as the two are highly conserved. Wild-type allele was differentiated from mutant by subjecting the polymerase chain reaction (PCR) amplified product to Msp 1 digestion and analysing the cleaved fragment as described earlier [6]. PCR amplified products from all the monkeys (10 from each species) were digested with the above restriction enzyme, the pattern of which enables one to genotype for wild-type, heterozygous or homozygous mutation. The PCR product (287 bp) of all 10 bonnets (Macaca radiata) and 10 baboons (Papio anubis) were resistant to Msp1 digestion, indicating the presence of the homozygous mutation. Only one out of 10 rhesus (Macaca mulatta) screened was heterozygous, the rest were homozygous for this mutation. Surprisingly, all the marmosets (Callith rix jacchus) were heterozygous (10). We then cloned the 287 bp amplified fragment into a T-tailed vector from at least three monkeys from the same group to rule out PCR-generated mistakes in the sequence. The comparison of the sequences is shown in Fig. 1 and the sequence is shown in Fig. 2.
Remarkably, double transition GG–AA was observed in all monkeys at position 801, 802 (counting from ATG – the initiation codon, GeneBank accession number L36033 of humans). In addition, C–A transversions were also observed in all monkeys at position 778 (Fig. 2, shown by arrows). An additional transition (G–A) at position 838 was seen in baboons only.
