Abstract
In this work we analyzed the in situ restriction endonucleases digestion on the nucleolar organizer region, NOR, localized in C chromosomes of Bradysia hygida. Neuroblast chromosomes in situ digestion with PstI revealed evident chromatin extraction at the NOR region on both homologous C chromosomes, while the digestion with EcoRI or HindIII removed only one of the C chromosomes NOR chromatin. The same results were observed when in situ digestion with HindIII+PstI and HindIII+EcoRI were processed. These data are correlated with the fragments size by hybridization of purified genomic DNA with Rhynchosciara americana rDNA. The cleavage with EcoRI or PstI produced fragments of high molecular weight, while the single digestion with HindIII and combined with EcoRI or PstI only showed fragments of low molecular weight. In conclusion, no correlation between the size of the fragment and the in situ digestion was observed. The accessibility of the enzyme at the NOR site can be facilitated when the chromatin is an open state and the region presents transcriptional activity, allowing the digestion and removal of the chromatin out of the chromosome.
