Action spectra for mitotic spindle destruction and anaphase delay following irradiation of the cytoplasm with an ultraviolet microbeam.

Abstract

Abstract— Previous workers have reported that, in a variety of cells, ultraviolet microbeam irradiation of cytoplasm adjacent to the mitotic spindle causes the spindle to diminish or disappear and have postulated that this effect is mediated by a spindle “poison” produced photochemically from a cytoplasmic precursor. In the present work, a microbeam action spectrum for this effect has been obtained to aid in the identification of this mediator material. A small portion of the cytoplasm of Ambystoma(salamander) tissue‐culture cells was irradiated in early metaphase with ultraviolet microbeams of various wavelengths and intensities but of the same diameter (8 μ). Spindle destruction was scored by observing diminution of its image as seen with a polarization microscope. In addition, the time of anaphase was recorded so that an action spectrum for anaphase delay was also obtained. These two action spectra are quite similar and are nearly parallel to the absorption spectrum of a tyrosine‐containing protein. A few proteins are discussed which might mediate this effect.