Cloning of 3′-end full-length cDNA encoding for MT-I and MT-III in yak and analysis of their sequences

Abstract Domestic yak (Bos grunniens) metallothionein-I (MT-I) and metallothionein-III (MT-III) cDNA 3′-end full-length sequences (331 and 378 bp; GenBank accession MT-I no. AY758557, MT-III no. DQ492300) from the total RNA of liver and brain tissues were amplified and cloned by reverse transcription polymerase chain reaction (RT-PCR) and 3′-rapid amplification of cDNA ends (RACE) using the primers YMT-I SP and M13 primers M4, and YMT-III SP and M13 primers M4, respectively, which included the MT-I (183 bp) coding sequence, MT-III (207 bp) cDNA coding sequences, and also the tailing signal AATAAA and Poly(A) at the 3′-ends of the MT-I and MT-III, respectively. The analyses showed that the yak cDNA sequence coding for MT-I protein was composed of 61 amino acids, including 20 cysteines having a conserved tripeptide structure, for example C–X–C, C–C–X–C–C, C–X–X–C and so on. The yak cDNA sequence coding for MT-III protein was composed of 68 amino acids, including 19 cysteines having both MT-III-specific conserved tripeptides and the same conserved tripeptides as MT-I, including T, CPCP, GEGAEA and so on. They were all comparatively conservative in molecular evolution. These structures indicated that MT-III had the same physiological functions regarding heavy metals (detoxification and so on) as MT-I, and also different specific functions from MT-I, including inhibition of neuron growth.