Transcription

Direct observation of DNA rotation during transcription by Escherichia coli RNA polymerase. Harada, Y. et al. Nature 409 , 113?115 (2001) [Contents page]

Several years ago Kazuhiko Kinosita Jr and colleagues used an elegant single-molecule imaging system to show direct rotation of the F1-ATPase. Now they've done it again, this time with a DNA-based motor ? RNA polymerase. They show, in real time, that single RNA polymerase molecules attached to a glass surface can rotate DNA for over 100 revolutions, and predict that this technique could help in resolving the individual steps of transcription.

Immunology

ICOS co-stimulatory receptor is essential for T-cell activation and function. Dong. C. et al. Nature 409 , 97?101 (2001) [Contents page]

ICOS is critical for CD40-mediated antibody class switching. McAdam, A. J. et al. Nature 409 , 102?105 (2001) [Contents page]

ICOS is essential for effective T-helper-cell responses. Tafuri, A. et al. Nature 409 , 105?109 (2001) [Contents page]

Optimal T-cell activation requires an antigen-specific signal as well as a co-stimulatory signal which influences T-cell proliferation, cytokine secretion and the development of effector functions. ICOS is a member of the CD28/CTLA4 family of costimulatory molecules, and is expressed on activated T cells. Its ligand, B7RP-1/B7H, is expressed on B cells and macrophages. So this pair of molecules does not seem to be involved in initial T-cell activation, but at a later stage during T-cell interactions with B cells and macrophages. To characterize the function of ICOS, three groups have now generated ICOS-deficient mice. They show that ICOS is essential for efficient T/B-cell interactions and for antibody production in response to T-cell-dependent antigens. Knockout mice have defective germinal centre formation and immunoglobulin class-switching, as well as decreased T-cell production of interleukin-4 and interleukin-13. Further work is required to understand the complex nature of costimulation so that therapies can be designed to treat immune-mediated diseases.

Apoptosis

An alternative, nonapoptotic form of programmed cell death. Sperandio, S. et al. Proc. Natl Acad. Sci. USA 97 , 14376?14381 (2000) [PubMed]

The terms 'apoptosis' and 'programmed cell death' are often used interchangeably, but this paper describes a form of programmed cell death that fails to fulfil the criteria for apoptosis. Christened paraptosis ('next to' or 'related to' apoptosis), this form of cell death has a distinct morphology and biochemistry to apoptosis, it shows no response to caspase inhibitors or Bcl-xL, and it is mediated by an Apaf-1-independent caspase-9 activity.