Alu tandem sequences inhibit GFP gene expression by triggering chromatin wrapping

Alu elements belonging to the short interspersed nuclear elements (SINE) of repetitive elements are present in more than one million copies which altogether represent 10% of the whole human genome. In this study, the roles ofAlu tandem sequences in the process of GFP gene (GFP) expression and packing into chromatin of its DNA were studied. To detect the effect ofAlu repeats on gene expression, different copies ofAlus were insertedGFP downstream respectively in pEGFP-C1 vector. We found thatAlu sequences decreased the amount ofGFP transcription, the percentage of GFP positive cells and the accessibility to DNase I in length-dependent manner. InsertingAlu caused the production of higher-molecular-mass RNA, indicatingAlu sequence did not induce premature transcriptional termination. Tight packing chromatins keep silent and resist to DNase I digestion, which is a general phenomenon. We suggested that head and tail tandemAlu sequences suppressedGFP expression in length dependent manner by triggering chromatin packing.