THE OCCURRENCE OF A MUTANT DIMERIZABLE HISTONE H5 IN JAPANESE-QUAIL ERYTHROCYTES

An allelic variant of linker histone H5 has been found in the erythroc ytes of Japanese quail (Coturnix japonica) descended from a small grou p of feral birds captured on the island of Hawaii. This variant sponta neously forms protein dimers in vitro in the absence of reducing agent s. That this depends upon the introduction of a sulfhydryl group (pres umably because of a cysteine substitution) is indicated by its reactio n with 2-nitro-5-thiocyanobenzoate and by its fluorescence after react ion with 4-aminosulfonyl-7-fluoro-2,1,3-benzoxadiazole. This is the fi rst reported example of cysteine in a vertebrate linker histone and of fers a specific reactive site for structural studies. A homozygous lin e for this form of H5 is being developed.