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In this article we will discuss about the mechanism of antisense ribosome.
Persistent search for novel vehicle for introducing antisense RNA into cells has become reality when Sweeney and Chaoyao (1998) developed antisense ribosomes in Tetrahymena thermophila.
This system allows expression of antisense gene present with rRNA genes and antisense RNA alters expression function as a part of a stable RNA molecule within large ribosomal subunit. Presence of antisense RNA molecule as a part of the ribosomal subunit never affects rRNA function.
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Primary sequence of ribosomal RNA (rRNA) reveals that there are variable region within rRNA. Most of the variable regions are likely to reside on the surface of the ribosome of which two variable in the large subunit rRNA are the most variable in size and considered that these variable regions may be functionally unimportant and their absence in prokaryotic suggests that they are not essential for translation process (Fig. 22.4).
Considering significance of these variable sequence fragments of genes in the antisense orientation were inserted into these sites. Insertion in only two variable sites showed significant antisense activity. The possible mechanism by which gene expression is suppressed by these antisense ribosomes, are due to blockage of translation rather than by causing destruction of mRNA.
According to Sweeney and Yao (1998) antisense RNA portion of the antisense ribosome appears as loop emerging out of the upper left of the large subunit. Since mRNA always have close proximity with ribosomes, base pairs between antisense RNA in ribosome and the target RNA takes place and prevent its translation. Meanwhile simultaneous translation of the mRNA proceeds without any interference.
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Several potential advantages have been suggested by this system compared with traditional antisense RNA approach. Some of the advantages that the inserted antisense RNA would be present at very high copy number. Second, the inserted antisense RNA is highly stable as rRNA third, antisense RNA, as part of the ribosome, would be in close proximity to mRNA inside the cell.
In addition, successful use of antisense ribosome in Thermophila presents the possibility of the potential vehicle may be well applicable in other eukaryotes and even presuming that this antisense ribosome vehicle could provide superior alternative to presently available antisense expression, besides allow for more than transient expression of the antisense molecule. Some of the surprising results reveal that replacing only 15% of the host rDNA with rDNA containing an antisense insert is sufficient to produce a potential antisense effect without compromising its original functions.
