Delineation of the Exact Transcription Termination Signal for Type 3 Polymerase III

Improvement of the CRISPR-Cpf1 system with ribozyme-processed crRNA

The recently discovered clustered regularly interspaced short palindromic repeats (CRISPR)-Cpf1 system expands the genome editing toolbox. This system exhibits several distinct features compared to the widely used CRISPR-Cas9 system, but has reduced gene editing efficiency. To optimize the CRISPR-Cpf1 (Cas12a) system, we report the inclusion of self-cleaving ribozymes that facilitate processing of the crRNA transcript to produce the precise guide molecule. Insertion of the 3'-terminal HDV ribozyme boosted the gene editing activity of the CRISPR-Cpf1 system ranging from 1.1 to 5.2 fold. We also demonstrate that this design can enhance CRISPR-based gene activation. We thus generated an improved CRISPR-Cpf1 system for more efficient gene editing and gene regulation.

A Single H1 Promoter Can Drive Both Guide RNA and Endonuclease Expression in the CRISPR-Cas9 System

The RNA-guided endonuclease Cas9 (CRISPR-Cas9) genome editing system has been widely used for biomedical research and holds great potential for therapeutic applications in eukaryotes. The conventional vector-based CRISPR-Cas9 delivery system requires two different RNA polymerase promoters for expression of the guide RNA (gRNA) and Cas9 endonuclease. The large size and relative complexity of such CRISPR transgene cassettes impede their broad implementation, especially in gene therapy applications with viral vectors that have a limited packaging capacity. Here, we report the design of a single-promoter-driven CRISPR-Cas9 system that uses the dual-polymerase (Pol II and Pol III) activity of the H1 promoter. This size reduction strategy of the vector insert provides a significant titer advantage in the lentiviral vector over the regular CRISPR system.

RNA Polymerase II Activity of Type 3 Pol III Promoters

In eukaryotes, three RNA polymerases (Pol I, II, and III) are responsible for the transcription of distinct subsets of genes. Gene-external type 3 Pol III promoters use defined transcription start and termination sites, and they are, therefore, widely used for small RNA expression, including short hairpin RNAs in RNAi applications and guide RNAs in CRISPR-Cas systems. We report that all three commonly used human Pol III promoters (7SK, U6, and H1) mediate luciferase reporter gene expression, which indicates Pol II activity, but to a different extent (H1 ≫ U6 > 7SK). We demonstrate that these promoters can recruit Pol II for transcribing extended messenger transcripts. Intriguingly, selective inhibition of Pol II stimulates the Pol III activity and vice versa, suggesting that two polymerase complexes compete for promoter usage. Pol II initiates transcription at the regular Pol III start site on the 7SK and U6 promoters, but Pol II transcription on the most active H1 promoter starts 8 nt upstream of the Pol III start site. This study provides functional evidence for the close relationship of Pol II and Pol III transcription. These mechanistic insights are important for optimal use of Pol III promoters, and they offer additional flexibility for biotechnology applications of these genetic elements.

RNA Interference Therapies for an HIV-1 Functional Cure

HIV-1 drug therapies can prevent disease progression but cannot eliminate HIV-1 viruses from an infected individual. While there is hope that elimination of HIV-1 can be achieved, several approaches to reach a functional cure (control of HIV-1 replication in the absence of drug therapy) are also under investigation. One of these approaches is the transplant of HIV-1 resistant cells expressing anti-HIV-1 RNAs, proteins or peptides. Small RNAs that use RNA interference pathways to target HIV-1 replication have emerged as competitive candidates for cell transplant therapy and have been included in all gene combinations that have so far entered clinical trials. Here, we review RNA interference pathways in mammalian cells and the design of therapeutic small RNAs that use these pathways to target pathogenic RNA sequences. Studies that have been performed to identify anti-HIV-1 RNA interference therapeutics are also reviewed and perspectives on their use in combination gene therapy to functionally cure HIV-1 infection are provided.