The gene is being actively transcribed, but no RNA accumulates. Post-transcriptional gene silencing also occurs when the transgene is also present in the viral genome. For example, a potato virus X genome bearing the GUS reporter gene infects wild type plants but will not infect plants that have an active GUS transgene. In the process, RNA oligomers of 21 to 23 nucleotides are produced. The silencing of a gene by the presence of a related gene is called cosuppression .
Different mechanisms lead to cosuppression .
The introduction of specific double-stranded RNAs into organisms provides a way of specifically inactivating the expression of certain genes. Further information Cosuppression is related to RIP protection against invasion of the genome. Cosuppression may also be related to the inhibitory effects of antisense RNA and RNA degradation .