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lncRNA - Long Non-coding RNAs
In humans, more than 80% of the genome gets transcribed. However, only around 2% of the genome codes for proteins. The remaining part produces non-cod…
Long non-coding RNAs or lncRNAs can regulate gene expression and other cellular processes. They are widespread and are found in plants, animals, bacteria, and viruses; however, they show low sequence conservation between different species.
LncRNAs are RNA transcripts longer than 200 nucleotides that are not translated into proteins; however, most are processed the same way as precursor mRNA through splicing and the addition of a 5’ cap and 3’ poly-A tail.
Compared to protein synthesis, RNA synthesis takes less energy and occurs more rapidly. As RNA is produced in the nucleus, it can be immediately used for gene regulation and can provide a faster response than proteins, which need to be imported from the cytoplasm.
LncRNA can perform their functions through several different mechanisms. When present near DNA, lncRNA can act as a scaffold for proteins by forming multiple stem-loop structures where proteins can bind and carry out their function, like chromatin-modifying proteins or transcriptional activators and repressors.
Like microRNA, lncRNA can act as guide RNA where its one part binds to various protein complexes whereas another part can selectively base pair with target DNA region and thereby helps in localization of the protein complexes.
LncRNA can act as alternative binding sites or sponges, sequestering some molecules away from their target location. For example, lncRNAs bind to microRNAs and prevent their interaction with their target mRNA.
LncRNA can base-pair with a complementary region in mRNA. This base-pairing can inhibit pre-mRNA splicing by hiding particular splice sites or can block the translation of mature mRNA.
Some lncRNA also carry exons and produce small peptides of unknown function.
LncRNAs are emerging as a significant player in additional cellular processes such as chromatin modifications and epigenetic regulation, as well as several diseases such as cancer and neurological diseases
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Q1: What are long non-coding RNAs and how do they differ from protein-coding genes?
Long non-coding RNAs (lncRNAs) are RNA transcripts longer than 200 nucleotides that are not translated into proteins. Unlike protein-coding genes, lncRNAs are processed similarly to precursor mRNA through splicing and addition of a 5' cap and 3' poly-A tail. They regulate gene expression and cellular processes across plants, animals, bacteria, and viruses, though they show low sequence conservation between species.
Q2: Why are lncRNAs more efficient than proteins for rapid cellular responses?
RNA synthesis requires less energy and occurs more rapidly than protein synthesis. Since lncRNA is produced in the nucleus, it can be immediately used for gene regulation, providing faster cellular responses than proteins, which must be synthesized and imported from the cytoplasm. This rapid availability makes lncRNAs effective regulators of time-sensitive cellular processes.
Q3: How do lncRNAs function as molecular scaffolds in gene regulation?
LncRNAs can act as scaffolds for proteins by forming multiple stem-loop structures where proteins bind and perform their functions. Chromatin-modifying proteins and transcriptional activators or repressors attach to these structures. This scaffolding mechanism allows lncRNAs to organize protein complexes and direct them to specific cellular locations for coordinated gene regulation.
Q4: What is the guide RNA mechanism used by lncRNAs?
Like microRNA, lncRNAs can act as guide RNA by binding to protein complexes with one region while another region selectively base pairs with target DNA sequences. This dual-binding capability helps localize protein complexes to specific genomic locations, enabling precise targeting of chromatin modifications and transcriptional regulation at desired genes.
Q5: How do lncRNAs act as molecular sponges to regulate gene expression?
LncRNAs can function as alternative binding sites or sponges, sequestering regulatory molecules away from their target locations. For example, lncRNAs bind to microRNAs and prevent their interaction with target mRNA, effectively blocking microRNA-mediated gene silencing. This sponge mechanism allows lncRNAs to modulate the activity of other regulatory molecules.
Q6: What are the different ways lncRNAs can inhibit mRNA translation and processing?
LncRNAs can base-pair with complementary regions in mRNA to inhibit pre-mRNA splicing by hiding particular splice sites, or they can block translation of mature mRNA. Some lncRNAs also carry exons and produce small peptides of unknown function. These mechanisms allow lncRNAs to regulate gene expression at both transcriptional and post-transcriptional levels.
Q7: Why are lncRNAs important in cancer development and treatment?
LncRNAs play important roles in cancer development, acting as tumor suppressors or promoters. Abnormal expression of specific lncRNAs occurs in tumor-specific patterns; for example, MALAT1 and XIST are associated with brain cancer, while HOTTIP and HOTAIR are linked to lung cancer. These cancer-associated lncRNAs serve as diagnostic biomarkers and potential therapeutic targets for cancer treatment.