Chromomycin A3

Chromomycin A3 (CMA₃) or Toyomycin is an anthraquinone antibiotic glycoside produced by the fermentation of a certain strain of Streptomyces griseus (No. 7).

Fluorescence properties

In the presence of Mg²⁺ ions, Chromomycin A₃ binds reversibly to DNA, preferentially to contiguous G/C base pairs.

When bound to DNA, Chromomycin A₃ has a maximum excitation wavelength of 445 nm (blue), and a maximum emission wavelength of 575 nm (yellow).

Uses

• in-vitro membrane-impermeant G/C-specific fluorescent DNA-binding dye.
• in-vitro antibiotic of gram-positive bacteria, through inhibition of the incorporation of P_i in the RNA.
• in-vitro anticancer drug that inhibits RNA synthesis.
• Evaluation of male fertility: Chromomycin A₃ and protamines compete for the same binding sites in the DNA, so CMA₃ positivity in spermatozoa reflects protamine deficiency (affecting sperm morphology and decreasing fertility).