Acid lability of deoxyribonucleic acids of some polytene chromosome regions of Rhynchosciara americana.

An analysis of profiles of Feulgen hydrolysis curves has been carried out in two heterochromatic (B-15 and C-11) and one euchromatic (C-1) regions of polytene chromosomes of salivary glands of 66 day old Rhynchosciara americana larvae. Differences among these three regions have been found mostly concerning the period of predominant apurinic acid breakdown including the "lag" phase of teh apurinic acid depolymerization. The hydrolysis time for which maximal Feulgen-DNA values are attained also differs when comparing the hetero- and euchromatic regions of the C chromosome and the heterochromatic regions C11 and B15 to each other. Different labilities of DNA to acid hydrolysis have therefore been demonstrated for these chromosome regions. This has been tentatively correlated with differences in non-histone proteins some of which are assumed to be involved in chromatin compactness. Others (probably not concerned with chromatin compactness) are suggested to be associated with certain specific DNA types which are known to occur in these chromosome regions.