Total Synthesis of Micrococcin P1 through Scalable Thiazole Forming Reactions of Cysteine Derivatives and Nitriles.

Thiopeptides are a class of natural products with untapped therapeutic potential. To expand the methods available for the scaled production of these antibiotics, we report the laboratory synthesis of micrococcin P1 showcasing thiazole forming reactions of cysteine derivatives and nitriles followed by oxidation. In most instances, this thiazole forming sequence does not require chromatography and proved scalable. Using this approach, 199 mg of micrococcin P1 was generated in a single synthetic sequence.

The mechanism of micro-RNA-mediated translation repression is determined by the promoter of the target gene.

MicroRNAs (miRNAs) are noncoding RNAs that base pair imperfectly to homologous regions in target mRNAs and negatively influence the synthesis of the corresponding proteins. Repression is mediated by a number of mechanisms, one of which is the direct inhibition of protein synthesis. Surprisingly, previous studies have suggested that two mutually exclusive mechanisms exist, one acting at the initiation phase of protein synthesis and the other at a postinitiation event. Here, we resolve this apparent dichotomy by demonstrating that the promoter used to transcribe the mRNA influences the type of miRNA-mediated translational repression. Transcripts derived from the SV40 promoter that contain let-7 target sites in their 3' UTRs are repressed at the initiation stage of translation, whereas essentially identical mRNAs derived from the TK promoter are repressed at a postinitiation step. We also show that there is a miR-34 target site within the 3' UTR of c-myc mRNA and that promoter dependency is also true for this endogenous 3' UTR. Overall, these data establish a link between the nuclear history of an mRNA and the mechanism of miRNA-mediated translational regulation in the cytoplasm.

Polypyrimidine tract binding protein regulates IRES-mediated gene expression during apoptosis.

During apoptosis there is a substantial reduction in the rate of protein synthesis, and yet some mRNAs avoid this translational inhibition. To determine the impact that receptor-mediated cell death has on the translational efficiency of a large number of mRNAs, translational profiling was performed on MCF7 cells treated with the apoptosis-inducing ligand TRAIL. Our data indicate that approximately 3% of mRNAs remain associated with the polysomes in apoptotic cells, and genes that are involved in transcription, chromatin modification/remodeling, and the Notch signaling pathway are particularly prevalent among the mRNAs that evade translational inhibition. Internal ribosome entry segments (IRESs) were identified in several of the mRNAs that remained associated with the polysomes during apoptosis, and, importantly, these IRESs functioned efficiently in apoptotic cells. Finally, the data showed that polypyrimidine tract binding protein (PTB, a known IRES trans-acting factor or ITAF) is pivotal in regulating the apoptotic process by controlling IRES function.