tRNA丰度是影响蛋白质二级结构形成的一个因素

从人和大肠杆菌蛋白质和DNA序列的统计分析，发现mRNA的对应一定蛋白质二级结构的m密码子片段(m=3，4，…，8)，当平均tRNA拷贝数高时(对于人高于11，对于大肠杆菌高于2．O)，偏好编码螺旋，而避免编码线团；当平均tRNA拷贝数低时，偏好性正好反过来．对于beta折叠，未发现和tRNA拷贝数有明显的统计关联．对大肠杆菌也研究了密码子频数与蛋白质二级结构的相关性，其间的关联比tRNA拷贝数与蛋白质二级结构的关联弱．因此，tRNA拷贝数与蛋白质二级结构的关联可能更为本质．机制目前尚不清楚．一种可能的解释是：tRNA丰度以某种方式影响了新生肽链的折叠，通过翻译精度的因素影响了蛋白质二级结构的形成．

tRNA Copy Number is a Factor Affecting the Formation of Protein Secondary Structure

From the statistical analyses of human and E.coli protein sequences we have found that the messenger RNA segment of m-codons (for m=3 to 8) with averagely high tRNA copy number (average copy number larger than 11 for human,larger than 2.0 for E.coli,respectively) preferably code for alpha helix but less code for coil and this structural preference/avoidance turns out contrary to the codons with low tRNA copy number.For beta strand the preference/avoidance tendency is not obvious and it shows oscillation with tRNA copy number of codons.The structural preference of codon tRNA copy number is much stronger than that of codon fractional frequency (for E.coli).The mechanism about these statistical relations is not clear yet. A possible explanation is:tRNA copy number is in some way influencing the local rate of translation extension and accuracy and therefore influencing the nascent peptide folding in local region.