Streptomyces genomes have a high G + C content and typically use an ATG or GTG codon to initiate protein synthesis. Although gene-finding tools perform well in low GC genomes, it is known that the accuracy in predicting a translational start site (TSS) is much less for high GC genomes. LipPks1 is a Streptomyces-derived, well-characterized modular polyketide synthase (PKS). Using this enzyme as a model, we experimentally investigated the effects of alternative TSSs using a heterologous host, Streptomyces venezuelae. One of the TSSs employed boosted the protein level by 59-fold and the product yield by 23-fold compared to the originally annotated start codon. Interestingly, a structural model of the PKS indicated the presence of a structural motif in the N-terminus, which may explain the observed different protein levels together with a proline and arginine-rich sequence that may inhibit translational initiation. This structure was also found in six other modular PKSs that utilize noncarboxylated starter substrates, which may guide the selection of optimal TSSs in conjunction with start-codon prediction software.

中文翻译：

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N端截短的LipPks1变体的异源基因表达表明模块化聚酮化合物合酶N端的功能至关重要的结构基序。

链霉菌的基因组具有较高的G + C含量，通常使用ATG或GTG密码子来启动蛋白质合成。尽管基因发现工具在低GC基因组中表现良好，但众所周知，对于高GC基因组，预测翻译起始位点（TSS）的准确性要低得多。LipPks1是链霉菌衍生的，特征明确的模块化聚酮化合物合酶（PKS）。使用这种酶作为模型，我们通过实验研究了异源宿主委内瑞拉链霉菌对其他TSS的影响。与最初注释的起始密码子相比，使用的一种TSS将蛋白质水平提高了59倍，并将产物收率提高了23倍。有趣的是，PKS的结构模型表明N中存在结构基序-末端，可以解释观察到的不同蛋白质水平以及脯氨酸和精氨酸丰富的序列，这些序列可能抑制翻译起始。在使用非羧化起始底物的其他六个模块化PKS中也发现了这种结构，可以结合起始密码子预测软件来指导最佳TSS的选择。