Gene silencing RNA ?
Ans. is 'c' i.e., miRNA According to recent sudies a very large number of genes do not encode proteins. Instead, their products play impoant regulatory functions. The most recently discovered among this class of genes are that encode for gene-silencing RNAs, i.e. RNAs that do not encode proteins but instead inhibit gene expression (unlike classical RNAs which encode for proteins) Two gene-silencing RNAs are: Micro RNAs (miRNAs) Small interfering RNAs (siRNAs) 1. Micro RNA (miRNAs) Because of their profound influence on gene regulation, miRNAs are assuming central impoance in understanding normal developmental pathways, as well as pathologic conditions, such as cancer. o By current estimates there are approximately 1000 genes in humons that encodes miRNAs. Transcription of miRNA gene produces primary miRNA transcripts, which is processed within the nucleus to form another structure, called pre-miRNA. Pre-miRNA is transpoed to cytoplasm by a transpoor (Expo) protein. Dicer (an enzyme) does the additional cutting of this pre-miRNA that are about 21-30 nucleotide in length (hence called "micro"). At this stage mRNA is still double stranded. Next, the miRNA unwinds, and single strands of this duplex are incorporated into a multiprotein complex called RNA-induced silencing complex (RISC). Base-pairing between the miRNA strand and it target mRNA (messenger RNA) directs RISC to either cause mRNA cleavage or repress its translation. In this way, the gene from which the target was derived is silenced (at a post-transcription level). A single miRNA can silence many target genes. 2. Small interfering RNAs (siRNAs) siRNAs work in similar manner as miRNA Unlike miRNA, siRNA precursors are introduced by investigators into cells. siRNA are becoming powerful tools for studying gene function and may in the future be used therapeutically to silence specific genes, such as oncogenes, whose products are involved in neoplastic transformation.
rRNA
tRNA
miRNA
None