Genetically engineering a yeast cell to take on functions of E.Coli cells (Read Details)?

An enzyme has to be produced, in order to do this a Yeast promoter is used in the E.coli cell, The Yeast promoter might not work necessarily why? If the promoter works it is noticed that the RNA strand that is being produced in transcription is 2x the length of the average RNA strand that is usually produced in transcription. Why is this likely? What are the likely 2 reasons?