链霉菌中一个多效性tRNA调节因子的靶基因研究

TTA is one of six triplets encoding the amino acid leucine in proteins. In Streptomyces bacteria, which are the most important source of antibiotics, bldA gene encodes the only tRNA species able to translate UUA codon efficiently. bldA is essential for antibiotics biosynthesis and sporulation but not for vegetative growth. Target genes through which bldA regulates antibiotics biosynthesis have been identified. In this project, we aimed to identify and study TTA-containing gene essential for sporulation.It was indicated by this work that adpAc, an S. coelicolor homologue of the A-factor dependent gene adpAg from S. griseus, complemented the bldH109 mutant at both single and multiple copies. The sequence of adpAc from the bldH109 mutant revealed a frameshift. A constructed in-frame deletion of adpAc showed a bald colony phenotype, and the mutant behaved like bldH109 in its pattern of extracellular signal exchange. Both adpAc and adpAg contain a TTA codon. A TTA-free version of adpAcwas engineered by replacing the TTA leucine codon with a cognate TTG leucine codon. The adpA (TTA→TTG) gene could partially restore aerial mycelium formation to a bldA mutant when it was followed in cis by the gene ornA, as in the natural chromosomal arrangement. This indicated that the UUA codon in adpAc mRNA is the principal target through which bldA regulates morphological differentiation. It also implied that the untranslated UUA codon in adpAc mRNA caused a polar effect on the downstream ornA, and that the poor translation of both genes contributes significantly to the deficiency of aerial mycelium formation in bldA mutants. Unlike the situation in S. griseus, adpAc transcription does not depend on the host's g-butyrolactone signalling system, at least in liquid cultures, and the promotor region of adpAc has significantly difference compared with adpAg. In addition, sigma factor BldN, which is a homologue of S. griseus sigma factor AdsA, a regulatory target of AdpAg in S. griseus,was present in the constructed adpAc null mutant of S.coelicolor. In a further difference between S. coelicolor and S.griseus, adpAc mutants was blocked in actinorhodin synthesis but not in undecylprodigiosin production.bldH (=adpAc) is the first S. coelicolor bld gene shown to contain a TTA codon, raising the possibility that it could provide the explanation for the morphological deficiency of bldA mutants. To this day, most cloned bld genes are regulatory genes, few gene involved in synthesis of diffusible extracellular signal was cloned. In this work, we have also identified a unique gene superfamily which negatively regulate sporulation and antibiotics synthesis in Streptomyces. And it was observed that the strain M145 might contain a strigent mutation in codon recognization...

由4 种碱基所构成的DNA和RNA组成64个三联体密码,具有21种编码意义，TTA是蛋白质中编码亮氨酸的6个三联体密码。