5 public questions tagged with this topic.
miRNA (microRNA) is involved in post-transcriptional gene silencing by binding to target mRNA and preventing its translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Human Genome Project and DNA Fingerprinting
Small interfering RNAs often guide heterochromatin formation in cis acting at locus producing homologous transcripts rather than diffusing. In fission yeast centromeric repeats transcribed into siRNA precursors processed into Ago1-loaded RITS remaining tethered to nascent transcript via base pairing, recruiting CLRC containing Clr4 methyltransferase to same domain. This cis-restricted recruitment ensures modification targeted exclusively to repeats producing dsRNA, not unrelated loci with limited similarity. In contrast cytoplasmic degradation by siRNAs acts in trans on distant transcripts. Dual modes explain epigenetic inheritance: transcriptional silencing cis, post-transcriptional trans turnover coordinated.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 4: siRNA Functions in Cis for Heterochromatin Assembly
Small interfering RNA pathway uses near-perfect complementarity guiding Argonaute degradation. Upon RISC loading and passenger ejection, guide strand pairs extensively with viral or transposon transcripts positioning scissile bond at Ago PIWI active site for cleavage between positions ten and eleven. Cleaved fragments rapidly degraded by Xrn1 5'-3' and exosome 3'-5', preventing translation. In plants, worms, fungi secondary amplification by RdRP generates additional siRNAs spreading silencing. Extensive pairing ensures specificity distinguishing siRNA from miRNA tolerating mismatches. This mechanism underlies knockdown technology using synthetic siRNA duplexes to deplete mRNAs for functional genomics and therapeutic gene silencing approaches widely.
Ref: NCBI Bookshelf, RNA Interference: siRNA Directed mRNA Degradation via RISC Cleavage
Small RNA sequencing is a tailored RNA-seq protocol focusing on 18 to 35 nucleotide regulatory RNAs isolated by gel size selection after adapter ligation. It specifically profiles microRNAs, endogenous siRNAs, piRNAs and other short non-coding RNAs that regulate gene silencing, translation and chromatin modification. Whole transcriptome sequencing, WTS, captures all RNAs, mRNA-seq enriches polyadenylated long coding transcripts, and targeted RNA-seq interrogates specific panels. Only small RNA-seq enriches and quantifies microRNAs and siRNAs, resolving length variants, isomiRs and differential expression of these regulatory molecules.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Small RNA sequencing is a specialized RNA-seq workflow designed for non-coding RNAs of 18–40 nucleotides such as microRNAs and small interfering RNAs. After total RNA extraction, RNAs are size-selected by gel or beads to enrich the small fraction, followed by ligation of 5′ and 3′ adaptors that exploit the characteristic 5′ phosphate and 3′ hydroxyl ends. Reverse transcription and PCR generate libraries that preserve strand information. Unlike mRNA sequencing which depletes small RNAs through poly(A) selection and size exclusion, this approach accurately quantifies miRNA expression, isoforms, and modifications.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
