Characterization of mutants of the vitamin D-binding protein/group-specific component: molecular evolution of GC*1A2 and GC*1A3, common in some Asian populations

A well defined polymorphism of vitamin D-binding/ group-specific component (GC) resides in exon 11. To characterize the molecular basis of GC^*1A2 and GC^*1A3, common in some Asian populations, we analyzed all coding exons amplified by the polymerase chain reaction. GC^*1F was divided into GC^*1F^c and GC^*1F^T by a C-T transition in the third nucleotide of the codon (TGC/T) for cysteine²⁸³ in exon 8. The sequencing of exons 8 and 11 showed that GC^*1A2 and GC^*1A3 had occurred on a GC^*1F^c genetic background. They also shared a substitution of cysteine (TGC) for arginine (CGC) at position 429 in exon 11. GC^*1A2 was characterized by having glycine (GGC) instead of serine (AGC) at position 335 in exon 9. GC^*1A2 evolved from GC^*1F^T by three mutational events, i.e. GC^*1F^TGC^*1F^cGC^*1A3 GC^*1A2. No evidence was obtained for the existence of the duplicated gene GC^*1F · 1A2 suggested by isoelectric focusing (IEF) of serum samples. The idea that the characteristic banding pattern of GC^*1F · 1A2 after IEF results from partial formation of a disulfide bond in the additional cysteine at position 429 is discussed.Deceased