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

The 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-ⅠNo.AY758557,MT-ⅢNo.DQ492300)from total RNA of liver and brain tissues were amplified and cloned by RT-PCR and 3'-RACE using the primers Y_(MT-Ⅰ)SP,Y_(MT-Ⅲ)SP and M13 primers M4, respectively,in which included MT-Ⅰ(183 bp)coding sequence,MT-Ⅲ(207 bp)cDNA coding sequence,and tailing signal AATAAA and Poly(A)at the 3'-end ofMT-Ⅰand MT-Ⅲ,respectively.The analyses showed that the yak cDNA sequence coding for MT-Ⅰprotein was composed of 61 amino acids,including 20 cysteines which had conserved tripetide structure,such as C-X-C,C-C-X-C-C, C-X-X-C,etc..The yak cDNA sequence coding for MT-Ⅲprotein was composed of 68 amino acids,including 19 cysteines which had both MT-Ⅲitself specific conserved tripetides and the same conserved tripetides with MT-Ⅰ,such as T,CPCP,GEGAEA,etc..They were all comparatively conservative in molecule evolution.These structures indicated that MT-Ⅲhad both the same physiological functions of heavy metals disintoxicating etc.with MT-Ⅰand the different specific functions,which inhibits the neurons growth,from MT-Ⅰ.