Promoter region is the regulatory portion of genes that controls transcription. Even if this portion is crucial for finely tuning protein expression, and is known that epigenetic alterations are dangerous for this control, poor knowledge are available about the role of point mutations. Indeed, several point mutations are identified in promoter region, their biological consequence is poorly understood and studied. Scientists of the University of Washington set up an array to screen the effect of mutation on promoter functionality. They analysed all possible point mutations into a core promoter: the construct presented the native sequence, followed by mutated promoter and the transcription fragment. Each construct was codified by a barcode; thus, after transcription, a quantitative measure of transcriptional activity was obtained. In this way, all mutations were screened and quantitatively characterized. A surprising result was that one mutation generated down-regulation of the expression, while two mutations didn’t alter so much the transcriptional activity. A possible explanation was that the interaction between DNA and polymerase was stabilized in presence of one mutation, reducing the capability to move onto DNA molecule. This experiment was performed in vitro with cellular extract. Scientists knew that the best way to accomplish this screening is to use transfected cell lines, and this will be the possible next step.