In order to get small molecular G-protein Rab3a, which serves to further investigate the interaction between Rab3a and other proteins, we amplified the full coding region of Rab3a cDNA by polymerase chain reaction(PCR), using human placenta total cDNA as template. The PCR products were recovered from gel electrophoresis and cloned into BamHI/XhoI site of vector pYESTrp2. The result of sequencing indicated that Rab3a insertion fragment included its initiation and termination codons in 5′- and 3′-terminal, respectively. Compared with the referred Rab3a, the amplified Rab3a beard five nonsense nucleotide mutations, but the deduced amino acid sequence from the nucleotide sequence were completely the same as the referred Rab3a protein, which demonstrated that the cloned placenta Rab3a was suitable for further study.

Metallothionein-3(MT-3), previously named as growth inhibitory factor, is the unique member of the metallothionein family that demonstrates bioactivity in vitro. To test if MT-3 dimerizes or polymerizes itself in vivo, the yeast two-hybrid system was established. In yeast two-hybrid system, MT-3 interacts with MT-3. A further two-hybrid test also indicated that MT-3 weakly interacted with its isoform MT-1. These primary results suggest that MT-3 probably trend to homodimerize or heterodimerize in vivo.