麦洼牦牛SRY基因克隆及序列分析

SRY是Y染色体上具体决定生物雄性性别的基因片段，是多数哺乳动物性别决定基因之一。本试验采用克隆测序SRY基因并结合生物信息学对其序列进行分析，利用软件Codon W分析麦洼牦牛、普通牛、绵羊、山羊、猪、小鼠、鸡和人该基因编码区的密码子偏好性。克隆测序得到SRY基因序列含1个690 bp的开放阅读框，共编码229个氨基酸；其编码区核苷酸序列与普通牛、绵羊、山羊、猪、小鼠、鸡、人相应序列间的一致性分别为99.9%、93.9%、91.2%、76.5%、43.3%、21.4%、69.1%。经聚类分析，麦洼牦牛首先与普通牛聚在一起，绵羊与山羊聚为一类，这两类相聚后再依次与猪、人、小鼠相聚，最后与鸡聚为一类，其结果与以往的生物学分类结果一致。该基因编码的蛋白质分子式为C₁₁₅₅H₁₈₂₇N₃₅₁O₃₄₈S₁₁，相对分子质量为2655.0，理论等电点PI为9.55，亲水性平均数为-0.855。其密码子偏好性分析显示，T3_s为0.2905、C3_s为0.3240、A3_s为0.3728、G3_s为0.2963，第3位碱基中出现G和C占第3位碱基总量的48%，同义密码子数为61。上述数据表明麦洼牦牛SRY基因编码序列与普通牛、绵羊、山羊、猪、人具有较高的一致性，在物种进化过程中较为保守。该基因对含A的密码子有较高的偏爱性，尽量避开以G结尾的密码子，且其所编码的蛋白质为亲水性蛋白。

Cloning and Sequence Analysis of SRY Gene in Maiwa Yak

SRY (sex-determining region on the Y chromosome) gene is located on Y chromosome of mammal and plays very important role of sex determination. With cloned and sequenced SRY gene, then analyzed the sequence by bioinformatics, meanwhile, knew the codon usage bias of SRY gene coding region in Maiwa yak, cattle, sheep, goats, pigs, mice, chicken and human. The results of the Maiwa yak SRY gene, contained an open reading frame(ORF) of 690 bp which it encoded 229 amino acids. The SRY nucleotide sequence of coding region was compared among Maiwa yak, cattle, sheep, goat, pig, mice, chicken and human. The identity of nucleotide sequences of the coding region of SRY gene between Maiwa yak and cattle, sheep, goat, pig, mice, chicken and human were 99.9%, 93.9%, 91.2%, 76.5%, 43.3%, 21.4%, 69.1%, respectively. Phylogenetic tree analysis showed that firstly Maiwa yak and cattle were belonged to a branch, sheep and goats were clustered into one group, and then these two categories were got together with pig, human and mice were belonged to a branch, finally clustered into a group with chicken, the results was consistent with the results of the conventional biological classification. After protein analysis resulted that gene encoded protein formula for molecular was C₁₁₅₅H₁₈₂₇N₃₅₁O₃₄₈S₁₁, molecular mass was 2655.0, theoretical PI was 9.55. the hydrophilic average -0.855. Codon preference analysis, the T3_s was 0.2905, the C3_s was 0.3240, the A3_s was 0.3728, G3_s was 0.2963, GC content of 48%, the number of synonymous codon was 61. Meanwhile,the reason that the SRY nucleotide sequences of the coding region was conservative and there was higher identity in Maiwa yak and cattle, sheep, goat, pig, human. The third nucleotide of the codon frequency of occurrence of A was greater than G. The SRY gene encoded a hydrophilic protein.