The HU protein of Deinococcus radiodurans imaged by AFM

Unlike eukaryotes, which have their genetic material within a nucleus, bacterial DNA is now known to be rather packed in diffuse, but not random, regions called nucleotides. But how are they organized ?
HU is an important, even essential, protein in some bacterial nucleotides. However, the cellular function of HU in DNA compaction has been controversial practically since its identification in the 1970s, notably because of its different behavior from one species to another. The AFM team of the MEM group, in collaboration with the DNA Lesions and Repair team of the VIC group, has made it possible to image for the first time the HU protein of Deinococcus radiodurans (DrHU) by Atomic Force Microscopy (AFM). This work highlights a brand new AFM image processing, based on a filter using the Laplacian operator, which allows the DrHU protein to be observed on native plasmids produced by E. coli as well as on generated linearized plasmids. This filter improves the visibility of single molecules beyond the limitation related to the AFM tip-sample convolution phenomenon. AFM images suggest two major functions of DrHU in the condensation, but also the decondensation of double-stranded DNA. The self-compacting dynamics of naked DNA, as well as the concentration of DrHU, are important parameters in the cellular performance of DrHU.

Nanoscale surface structures of DNA bound to Deinococcus radiodurans HU unveiled by atomic force microscopy. Chen SWW, Banneville AS, Teulon JM, Timmins J and Pellequer JL. Nanoscale 2020 ;12(44):22628-22638

Contact : Jean-Luc Pellequer (Methods and Electron Microscopy group)