Small RNA

Small RNA

Small RNA refers to a class of short ribonucleic acid (RNA) molecules that are involved in the regulation of gene expression and other cellular processes. These molecules are typically 20-30 nucleotides in length and play crucial roles in various biological functions, including gene silencing, RNA interference, and the regulation of developmental processes.

Types of Small RNA

Small RNAs can be categorized into several types based on their biogenesis and function:

• MicroRNA (miRNA): These are endogenous, non-coding RNA molecules that regulate gene expression by binding to complementary sequences on target messenger RNA (mRNA) transcripts, usually resulting in gene silencing.

• Small Interfering RNA (siRNA): These are often exogenous double-stranded RNA molecules that are processed into small fragments and incorporated into the RNA-induced silencing complex (RISC) to mediate the degradation of complementary mRNA.

• Piwi-interacting RNA (piRNA): These are a distinct class of small RNA molecules that interact with Piwi proteins and are primarily involved in the regulation of transposons in germ cells.

• Small Nuclear RNA (snRNA): These are involved in the splicing of pre-mRNA and are components of the spliceosome.

• Small Nucleolar RNA (snoRNA): These are primarily involved in the chemical modification of other RNA molecules, such as ribosomal RNA (rRNA).

Biogenesis of Small RNA

The biogenesis of small RNA involves several key steps:

1. Transcription: Small RNAs are transcribed from DNA by RNA polymerase II or RNA polymerase III.

2. Processing: The primary transcripts are processed into mature small RNA molecules. For example, miRNAs are processed from primary miRNA (pri-miRNA) to precursor miRNA (pre-miRNA) and finally to mature miRNA by the action of the Drosha and Dicer enzymes.

3. Incorporation into RISC: Mature small RNAs are incorporated into the RNA-induced silencing complex (RISC), where they guide the complex to target mRNA molecules for silencing.

Functions of Small RNA

Small RNAs are involved in a variety of cellular processes, including:

• Gene Regulation: By binding to target mRNAs, small RNAs can inhibit translation or lead to mRNA degradation, thus regulating gene expression.

• Defense Mechanisms: Small RNAs play a role in defending against viral infections and the proliferation of transposable elements.

• Developmental Timing: Certain small RNAs are involved in the regulation of developmental timing and cell differentiation.

Research and Applications

Research into small RNAs has expanded our understanding of gene regulation and has led to the development of new therapeutic approaches, such as RNA interference (RNAi) technology, which is used to silence specific genes in research and clinical settings.

Also see

• RNA interference
• Gene silencing
• MicroRNA
• RNA-induced silencing complex
• Transposon