Unique translation initiation of mRNAs-containing TISU element.

Translation Initiator of Short 5' UTR (TISU) is a unique regulatory element of both transcription and translation initiation. It is present in a sizable number of genes with basic cellular functions and a very short untranslated region (5' UTR). Here, we investigated translation initiation from short 5' UTR mRNAs with AUG in various contexts. Reducing 5' UTR length to the minimal functional size increases leaky scanning from weak and strong initiators but hardly affects translation initiation and ribosomal binding directed by TISU. Ribosome interaction with TISU mRNA is cap dependent and involves AUG downstream nucleotides that compensate for the absent 5' UTR contacts. Interestingly, eIF1 inhibits cap-proximal AUG selection within weak or strong contexts but not within TISU. Furthermore, TISU-directed translation is unaffected by inhibition of the RNA helicase eIF4A. Thus, TISU directs efficient cap-dependent translation initiation without scanning, a mechanism that would be advantageous when intracellular levels of eIF1 and eIF4A fluctuate.

Characterization of sINR, a strict version of the Initiator core promoter element.

The proximal promoter consists of binding sites for transcription regulators and a core promoter. We identified an overrepresented motif in the proximal promoter of human genes with an Initiator (INR) positional bias. The core of the motif fits the INR consensus but its sequence is more strict and flanked by additional conserved sequences. This strict INR (sINR) is enriched in TATA-less genes that belong to specific functional categories. Analysis of the sINR-containing DHX9 and ATP5F1 genes showed that the entire sINR sequence, including the strict core and the conserved flanking sequences, is important for transcription. A conventional INR sequence could not substitute for DHX9 sINR whereas, sINR could replace a conventional INR. The minimal region required to create the major TSS of the DHX9 promoter includes the sINR and an upstream Sp1 site. In a heterologous context, sINR substituted for the TATA box when positioned downstream to several Sp1 sites. Consistent with that the majority of sINR promoters contain at least one Sp1 site. Thus, sINR is a TATA-less-specific INR that functions in cooperation with Sp1. These findings support the idea that the INR is a family of related core promoter motifs.

TAF4/4b x TAF12 displays a unique mode of DNA binding and is required for core promoter function of a subset of genes.

The major core promoter-binding factor in polymerase II transcription machinery is TFIID, a complex consisting of TBP, the TATA box-binding protein, and 13 to 14 TBP-associated factors (TAFs). Previously we found that the histone H2A-like TAF paralogs TAF4 and TAF4b possess DNA-binding activity. Whether TAF4/TAF4b DNA binding directs TFIID to a specific core promoter element or facilitates TFIID binding to established core promoter elements is not known. Here we analyzed the mode of TAF4b.TAF12 DNA binding and show that this complex binds DNA with high affinity. The DNA length required for optimal binding is approximately 70 bp. Although the complex displays a weak sequence preference, the nucleotide composition is less important than the length of the DNA for high affinity binding. Comparative expression profiling of wild-type and a DNA-binding mutant of TAF4 revealed common core promoter features in the down-regulated genes that include a TATA-box and an Initiator. Further examination of the PEL98 gene from this group showed diminished Initiator activity and TFIID occupancy in TAF4 DNA-binding mutant cells. These findings suggest that DNA binding by TAF4/4b-TAF12 facilitates the association of TFIID with the core promoter of a subset of genes.

Links between core promoter and basic gene features influence gene expression.

BACKGROUND: Diversity in rates of gene expression is essential for basic cell functions and is controlled by a variety of intricate mechanisms. Revealing general mechanisms that control gene expression is important for understanding normal and pathological cell functions and for improving the design of expression systems. Here we analyzed the relationship between general features of genes and their contribution to expression levels. RESULTS: Genes were divided into four groups according to their core promoter type and their characteristics analyzed statistically. Surprisingly we found that small variations in the TATA box are linked to large differences in gene length. Genes containing canonical TATA are generally short whereas long genes are associated with either non-canonical TATA or TATA-less promoters. These differences in gene length are primarily determined by the size and number of introns. Generally, gene expression was found to be tightly correlated with the strength of the TATA-box. However significant reduction in gene expression levels were linked with long TATA-containing genes (canonical and non-canonical) whereas intron length hardly affected the expression of TATA-less genes. Interestingly, features associated with high translation are prevalent in TATA-containing genes suggesting that their protein production is also more efficient. CONCLUSION: Our results suggest that interplay between core promoter type and gene size can generate significant diversity in gene expression.

Overcoming RNAi transduction in leukocytes using targeted and stabilized nanoparticles.

RNAi-based approaches have contributed significantly to the improved understanding of gene expression and function in vitro. The ability to apply these strategies in vivo to validate the role of specific genes in normal or pathological conditions, and to induce gene silencing, has led to new possibilities for using RNAi as a novel therapeutic modality. However, the translation of RNAi from an effective genomic tool into clinical applications has been hindered by the challenge of delivering RNAi molecules to their target tissues by systemic administration, particularly to hematopoietic cells. This feature review describes the current systemic RNAi delivery platforms targeted to leukocytes, with a focus on the integrin-targeted stabilized nanoparticles strategy, which uses leukocyte integrins for the delivery of siRNAs exclusively to cells of the immune system.

A translation initiation element specific to mRNAs with very short 5'UTR that also regulates transcription.

Transcription is controlled by cis regulatory elements, which if localized downstream to the transcriptional start site (TSS), in the 5'UTR, could influence translation as well. However presently there is little evidence for such composite regulatory elements. We have identified by computational analysis an abundant element located downstream to the TSS up to position +30, which controls both transcription and translation. This element has an invariable ATG sequence, which serves as the translation initiation codon in 64% of the genes bearing it. In these genes the initiating AUG is preceded by an extremely short 5'UTR. We show that translation in vitro and in vivo is initiated exclusively from the AUG of this motif, and that the AUG flanking sequences create a strong translation initiation context. This motif is distinguished from the well-known Kozak in its unique ability to direct efficient and accurate translation initiation from mRNAs with a very short 5'UTR. We therefore named it TISU for Translation Initiator of Short 5'UTR. Interestingly, this translation initiation element is also an essential transcription regulatory element of Yin Yang 1. Our characterization of a common transcription and translation element points to a link between mammalian transcription and translation initiation.