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Optical tweezers & single molecule fluorescence

We are developing an Optical Tweezers with single molecule fluorescence imaging capability instrument for use in single molecule biophysics experiments. Our aim is to characterize viral molecular motors (RNA polymerase, Hexameric packaging motor) on single molecule level. Our collaborators include Roman Tuma (University of Leeds, UK) and Dennis Bamford (Institute of Biotechnology, University of Helsinki).

For more information, please contact: Kalle Hanhijärvi

DNA ejection from an archaeal virus His1

We have measured DNA ejection from an archaeal virus His1 in vitro using TIRF microscopy.  Ejection is inhibited by increasing external osmotic pressure and mono- or divalent salt concentration.

A – Single event ejection traces measured at 58 fps. B – Purified His1 dsDNA genome on glass. C – Ejection in TRIS buffer.

Number of ejected molecules per field of view with varying buffer conditions. A – PEG300-induced osmotic pressure. B – Magnesium chloride. C –  Sodium chloride.

K. J. Hanhijärvi, G. Ziedaite, M. K. Pietilä, E. Hæggström, and D. H. Bamford, “DNA ejection from an archaeal virus – single-molecule approach”, Biophysical Journal 104(10), pp. 2264-2272, 2013. doi:10.1016/j.bpj.2013.03.061

For more information please contact: Kalle Hanhijärvi, Ida Holopainen

Dual-trap optical tweezers with real-time force clamp

A ~16 um long DNA-molecule is tethered between optically trapped plastic beads. Beads are held by a stationary trap (lower blue cross-hairs) and a steerable trap (upper green cross-hairs). The graphs on the right show the measured force (red) and the force set-point (blue) (top), the distance between the traps (middle), and the force-extension curve with a green cross indicating the current value (bottom).

Anders E. Wallin, Heikki Ojala, Gabija Ziedaite, and Edward Hæggström. “Dual-trap optical tweezers with real-time force clamp control” Rev. Sci. Instrum. 82, 083102 (2011); doi:10.1063/1.3615309 (7 pages).