7-amino-4-methylcoumarin-3-acetic acid-conjugated streptavidin permits simultaneous flow cytometry analysis of either three cell surface antigens or one cell surface antigen as a function of RNA and DNA content.

We have investigated the use of the new coumarin dye AMCA (7-amino-4-methylcoumarin-3-acetic acid), as a fluorochrome for multiple color fluorescence analysis by flow cytometry. AMCA is now commercially available as a streptavidin conjugate. Its excitation wavelength is optimal at 351/364 nm with a UV argon ion laser and it emits optimally in the blue at 450 nm. AMCA-conjugated streptavidin yields a fluorescence intensity comparable to that obtained with FITC-streptavidin. The emission spectrum of AMCA does not interfere with that of FITC and phycoerythrin and thus permits triple color analysis of cell surface antigens without requiring the need for important electronic compensation. A unique feature of AMCA conjugates was the possibility to determine the expression of a surface antigen as a function of cellular RNA and DNA levels stained with acridine orange. AMCA conjugates will thus facilitate multiple color analysis by flow cytometry.