Correlation between constitutive heterochromatin and restriction enzyme resistant chromatin in Arcyptera tornosi (Orthoptera).

Fixed mitotic chromosomes of A. tornosi have been analysed by means of C-banding, DA-DAPI and Chromomicin A3 fluorescence, as well as by digestion in situ with Alu I, Hae III, Hinf I and Hind III restriction endonucleases. From the results obtained at least nine types of chromatin can be distinguished in A. tornosi. Some C-band positive areas (constitutive heterochromatin) which show a characteristic fluorescence pattern are digested by specific endonucleases, whilst others are undigested. C-band negative areas (euchromatin) are digested by some restriction endonucleases but not by others. Regions digested are supposed to contain highly repetitive DNAs. It is noteworthy, however, that the heterochromatin associated with NORs is not attacked by any of the enzymes we used, while regions believed to contain AT-rich DNA (DA-DAPI positive) are digested by Hae III that cleaves the GG decreases CC base sequence target.