Transgene incorporation in plant genome does not mean that the gene will be active and will show expression at the required level. It is often the case that transgenic plants do not exhibit the activity of the gene introduced. Gene expression is known to be dependent on many factors such as: chimeric gene structure, proper and stable integration to the genome and proper transcription and translation. The knowledge of transgene regulation is essential for the understanding of the transcription and translation mechanisms. Each plazmid component is vital for later transgene expression. This refers to the size of T-DNA introduced, location of particular elements, leader sequences length, AUG sequences, introns presence, optimum coding gene synthesis, removal of RNA instability signals and many other possible modifications.