There is provided a method of inhibiting gene expression by locating a 5'-5 donor splicing site sequence in the 3' UTR of a gene or within coding sequence containing the stop codon of a gene. Stability of homologous mRNA in trans is also adversely affected leading to a reduction in expression. A polynucleotide containing a 5'-donor splicing site sequence in either coding sequence containing the stop codon or the 3' UTR is also provided and in one embodiment is in the form of a vector. The 5'-donor splicing site sequence can be present in multiple copies, for example as a tandem repeat. In one embodiment the 5-donor splicing site sequence has the sequence 5'-MAGGTRAGTA-3' where M is A or C and R is A or G.