Absorption spectrum of Feulgen-stained polytene chromosomes of Drosophila melanogaster.

Hetero- and euchromatic polytene chromosome regions of early and fully grown larvae of Drosophila melanogaster had their Feulgen absorption curves determined cytophotometrically. Hydrolysis conditions adequate to induce maximal DNA depurination were used. No differences in curve shapes specially concerning the absorption shoulder at the 520 less than or equal to lambda less than or equal to 550 nm spectral range were detected with advancing polytenization or when comparing the absorption patterns for the hetero- and euchromatic regions to each other. It is considered that prominence of the Feulgen absorption shoulder could be related to the amount of Schiff molecules di-substituted with apurinic acid aldehydes and to the relatively larger resistance of these apurinic acid fragments towards solubilization with acid hydrolysis due to their binding to nuclear proteins. It is therefore assumed that no significant differences owing to the above-cited factors exist for the chromosome regions analyzed at 2 phases of the polytenization process. Consequently, the replication of reiterated sequences from the main band DNA which occurs in polytene chromosome regions of Drosophila melanogaster appears not to affect the Feulgen absorption spectrum of this material.