As an illustration of the versatility of the present approach this simple system was simulated. Our model system, illustrated in Figure 2, consisted of a rod-shaped cell with a nucleus at its centre. Inside the nucleus, a gene is switched on at time t = 0, for 20 minutes. Transcription events then take place, generating mRNA molecules. These mRNA molecules diffuse out of the nucleus and encounter ribosomes which translate them into proteins. These proteins are considered to be tagged for the nucleus and therefore are allowed to pass through the membrane and accumulate in the nucleus. Both the mRNA and the protein have ubiquitination/destruction pathways that regulate their lifetime inside the cell such that the system reaches a steady state with a finite concentration of mRNA and protein. At time t = 20 min the gene is turned off and the concentration of mRNA and protein drops rapidly.