Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) systems, notably the CRISPR-associated protein 13 (Cas13), are guided by a synthetic guide ribonucleic acid (guide RNA) to target specific sequences on precursor messenger ribonucleic acid (pre-messenger RNA). Cas13 is a type of RNA-guided endonuclease that is part of the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) system. Unlike other Cas proteins, which typically target DNA, Cas13 specifically targets RNA. This makes it a valuable tool in genetic research and biotechnology, particularly for applications involving RNA detection and editing. Cas13 can be used to modify RNA sequences, which can have implications in gene therapy for genetic diseases. It can be utilized in diagnostics to detect viral RNA, such as that from the SARS-CoV-2 virus, which causes COVID-19. Chemically, Cas13 functions by recognizing specific RNA sequences and cleaving them, which can lead to the degradation of harmful RNA sequences in pathogens. Holistically, using Cas13 in therapies may not only target the disease at the molecular level but also potentially reduce the overall burden of disease in the body by preventing the replication of harmful RNA viruses. This occurs after transcription, meaning it modifies ribonucleic acid that has already been copied from deoxyribonucleic acid (DNA). The guide ribonucleic acid's 'spacer' region base-pairs with the target ribonucleic acid, providing specificity through Watson-Crick base pairing (adenine-uracil, guanine-cytosine). This allows for precise modulation of ribonucleic acid splicing, the process where non-coding regions (introns) are removed and coding regions (exons) are joined together. Exons are segments of DNA that contain the information needed to code for proteins. They are the sequences that are expressed and translated into proteins.Function: After a gene is transcribed into messenger RNA (mRNA), the exons are spliced together to form the final mRNA molecule that will be translated into a protein. Mutations in exons can lead to significant changes in protein structure and function, potentially leading to diseases. Introns are segments of DNA that do not code for proteins. They are found between exons in a gene. Introns are removed from the mRNA transcript during a process called splicing. While they do not code for proteins, they can play regulatory roles and influence gene expression and the timing of protein production. Mutations or errors in splicing can disrupt the regulation of gene expression and lead to diseases. When a gene is expressed, the DNA is transcribed into mRNA, which contains both introns and exons. The introns are removed through splicing, leaving the exons to be translated into proteins. Mutations in exons can lead to malfunctioning proteins, affecting biological functions and potentially causing diseases like cancer or genetic disorders.The balance between exons and introns is crucial for proper gene regulation. Disruptions in splicing or mutations can alter cellular functions and contribute to disease development.Cas13's ability to bind and, if catalytically active, cleave ribonucleic acid is due to its Higher Eukaryotes and Prokaryotes Nucleotide-binding (HEPN) domains, which are activated upon correct guide ribonucleic acid-target pairing. Final Effect: Enables highly specific and programmable editing of RNA molecules, particularly for controlling which exons are included in mature mRNA. Why Important: This precision allows scientists to directly alter gene expression and protein diversity after transcription, opening new avenues for treating diseases caused by splicing errors or aberrant RNA.