The Hyderabad-based Centre for Cellular and Molecular Biology (CCMB) has generated recombinant viruses harbouring an RNAi construct to use as a "sensor" to screen the virus genome by knowing out each open reading frame (ORF) of virus.

A paper published by CCMB scientists, led by Utpal Bhadra observed that "this method of screening by using sensors will also reveal the ORFs importance for virus replication and virulence."

Giving background for the new research, the scientists said the strategy of producing transgenic silkworms and double-stranded RNA (dsRNA) against one of the viral genes had failed in controlling infection. This raised the possibility that "like many other viruses Baculoviruses could also bypass or overcome RNAi-mediated immune system of their host by employing suppressors of RNAi."

The research, which started during 2004-2005, was undertaken to determine the genes which could contribute to prevent viral infection. The molecular characterisation of such genes may help in developing anti-viral drugs, the scientists felt.

"Ribonucleic acid (RNA) silencing serves as an adaptive antiviral defence system. Recent discoveries in our laboratories and elsewhere indicate that a similar silencing mechanism is at work to silence different animals' viruses," the scientists revealed.

The scientists developed baculovirs gene chip using 158 ORFs from baculovirus genome to target a model viral genome. The new siRNA (short interfering RNA or silencing RNA) delivery vectors, which the scientists generated, mitigated the baculovirus infection in sf9 (spodoptera frugiperda) cell culture. It was now established that Dicer-2 was able to initiate the small RNA-guided RNA inference antiviral immunity in Drosophila against the Flock House Virus (FHV). This immunity system was a capable of raid virus clearance in the absence of FHV-B2 proteins which "act as a broad spectrum RNAi inhibitor," the scientists pointed out.

They further said that they had three different RNA viruses last year. They were "FHV, Drosophila C Viruses and Cricket Paralysis virus." They also exerted significant influence on the host of chromatin organisation during active infection. "Recently we have found that a significant amount of FHV-B2 proteins enters the nucleus for making such changes in chromatin organisation that are associated with repeat-induced silencing," they added.