Loading video... VIDEO: To reconstruct a 3D image of the human Mediator-bound transcription pre-initiation complex, researchers first captured hundreds of thousands of images of the Med-PIC complex. They then used computational methods to... view more Credit: Northwestern University For the first time ever, a Northwestern University-led research team has peered inside a human cell to view a multi-subunit machine responsible for regulating gene expression. Called the Mediator-bound pre-initiation complex (Med-PIC), the structure is a key player in determining which genes are activated and which are suppressed. Mediator helps position the rest of the complex -- RNA polymerase II and the general transcription factors -- at the beginning of genes that the cell wants to transcribe.