Question

give two examples of homologous interference and explain in full detail how it contributes to self limiting of viruses

Answer 1

The two homologous RNA components of the multiple component tobacco rattle virus  undergo competition leading to interference undergo competition leading to interference of viral RNA replication by short RNA molecules utilizing the same replicase as the parent viral RNA has been reported for vesicular stomatitis virus . It has been argued that interference between homologous RNA molecules is due to competition by the smaller RNA species for the viral replicase. The phenomenon has also been reported for the replication of QB-RSA in vitro (3). No such mechanism has been reported for plant viruses, even though multiple component systems arc common and might be expect’ed to demonstrate a similar phenomenon. Homologous interference of the L-RNA infectivity by the short rods was demonstrated by assaying mixtures of the separated components at increasing short to long ratios. Unstable form infection (LRNA) produced maximal numbers of local lesions on cucumber

genetic competition may not be the only factor operative in immunity of lysogenic bacteria. in 1956 scientist  found that a lysogenic bacterium resists superinfection with phage P2 if it carries prophage P2 at a secondary nonpreferred site on its chromosome. This led to the suggestion that "immunity is physiologically controlled (by some product of the prophage) and not the result of competition for the standard site of prophage attachment." In addition to "homologous immunity," Lederberg (1957) has shown conclusively that E. coli or Shigella dysenteriae lysogenic for phages P2 or P1 also fail to support multiplication of certain heterologous bacteriophages. Growth of superinfecting phage is suppressed at some stage following attachment. It is difficult to invoke a genetic basis for this type of resistance to infection which, in many respects,resembles interference (mutual exclusion) between unrelated viruses. As one tentative hypothesis, Lederberg suggests that a specific inhibitor, possibly deoxyribonuclease (DNase), may be formed by the host cell in response to the superinfecting phage.