Question

MicroRNAs have an important function in gene regulation. What endoribonuclease is responsible for cleaving pre-miRNA into dsRNA (1 point)

What is the name of the enzyme that cleaves pre-miRNA into an 80-nucleotide precursor (1 point)?

Describe how miRNA can suppress gene expression (3 points)

Answer 1

Endoribonucleases are ribonuclease endonucleases that are responsible for cleaving single or double stranded DNA molecules. The cleavage of pre-miRNA into double stranded RNA fragments occurs in the cytoplasm. And is carried out by an enzyme called as Dicer or Endoribonuclease Dicer. Dicer belongs to the family of RNase III .

The enzyme that cleaves pre-miRNA into an 80-nucleotide precursor is RNAase III Drosha. This helps in maturation of miRNA as Drosha cleaves pre-miRNA's to release a hairpin structure called precursor mi-RNA.

miRNA or micro-RNA are small non coding genes which function in RNA silencing and post transcriptional regulation of the gene expression.

• They bind to the untranslated 3' region (3' UTR) of their target mRNA sequences and repress the production of protein. miRNA takes part in to form (RISC) RNA-induced silencing complex which is composed of an Argonaute (AGO) protein and a miRNA molecule.
• This complex helps miRNA to recognize their mRNA targets through base pairing and also de-attachment / reattachment to different targets.
• Such miRISC hinder the translation or act as an enhancer in degradation of mRNA.
• Hence there would be alteration in the gene sequences ultimately leading to suppression of gene expression.