siRNA for inhibiting HIV-I replication

RNAi is fast emerging as a wonderful tool for inhibiting gene expression in a sequence specific manner. The applications of this technology are two-fold: to study gene function, and use as a therapeutic agent in treating many diseases. As a therapeutic agent it finds applications in antiviral treatments because RNAi has been shown to successfully [...]

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piRNAs

Piwi-interacting RNAs (piRNA) are a class small of RNA molecules that are expressed uniquely in mammalian spermatogenic cell lines. These are 26–31 nucleotides long and bigger that miRNAs and siRNAs. They are so named because of their capability of forming RNA-protein complexes with Piwi proteins. Piwi proteins are part of the family of Argonaute [...]

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rRNA

Ribosomal RNAs (rRNAs) constitute ribosomes where protein synthesis occurs. rRNA and ribosomal proteins combine to form ribosomes. Both prokaryotic and eukaryotic rRNA are made from longer precursors called preribosomal RNAs, or pre-rRNA .
In bacteria, a single 30S, 6500 nucleotides long, RNA precursor, after processing, makes 16S, 23S and 5S rRNAs. RNA at both ends of [...]

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Poly(A) tail

At the 3′ end, most eukaryotic mRNAs have a string of 80-250 adenylate residues called the poly(A) tail. The poly(A) tail is added in a multistep process after the mRNA transcript has been synthesized. Two sequences are required for cleavage and polyadenylation (addition of ploy(A) tail) of the mRNA: 1) A highly conserved polyadenylation signal [...]

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Eukaryotic mRNA: 5′ cap and 3′ poly(A) tail

The 5′ end of eukaryotic mRNA is capped with a guanine nucleotide (which is methylated forming 7-methyguanosine). The cap (5′-G) is added to the mRNA after transcription. The addition of 5′ G is catalyzed by a nuclear enzyme, guanylyl transferase. The cap is linked to the 5′ terminus of the mRNA through an unusual 5′,5′-triphospahe [...]

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mRNA: Leader and trailer sequences

All mRNAs contains two regions. A coding region which consists of a series of triplet codons representing the amino acid sequence of the coded protein, starting with and AUG (initiation codon) and ending with a termination codon. This is referred to as the open reading frame (ORF). Extra regions are present at both the 5′ [...]

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mRNA

mRNA encodes the amino acid sequence of the polypeptide specified by a gene. The function of mRNA is the same in all cells, but there are some differences in the synthesis and structure of prokaryotic and eukaryotic mRNA.
1) In bacteria, mRNA is transcribed and translated in the single cellular compartment, i.e, there is no spatial [...]

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tRNA contd…

 
The so-called extra arm is the most variable part of tRNA molecule, and on the basis of nature of the extra arm, tRNAs have been divided into two classes:
1) Class 1 tRNAs: They have a smaller extra arm, which is 3-5 bases long. They represent approximately 75% of all tRNAs.
2) Class 2 tRNAs: [...]

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tRNA

tRNAs are transcribed as larger precursors, and these are finally cleaved into mature 4S tRNA molecules. tRNAs are generally rich in “unusual” bases, which are created following transcription. This illustrates the concept of posttranscriptional modification. The “cloverleaf” model of tRNA was proposed by Robert Holley.
All the tRNAs contain …CCA-3′ sequence at the 3′ end, and [...]

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tRNA (transfer RNA): The “Adapter”

The tRNA or the “adapter” is 74 to 95 bases long ribonucleic acid. It has two crucial properties:
1) It represents a single amino acid; the amino acid is covalently linked to the tRNA and carried to the site of protein synthesis (ribosomes).
2) It contains the anticodon , a trinucletide sequence, which is complementary to the [...]

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