IN-VIVO OBSERVATION OF THE PUFF-SPECIFIC PROTEIN NO-ON TRANSIENT-A (NONA) IN NUCLEI OF DROSOPHILA EMBRYOS

The spatial distribution of no-on transient A (NONA), a protein associ ated with specific puffs on polytene chromosomes, was followed in nucl ei of living Drosophila embryos by microinjection of fluorescently lab eled monoclonal antibody to NONA. The injected antibodies remained act ive until the larval stage, revealing the distribution of the NONA pro tein throughout embryogenesis. Most injected animals completed embryon ic development and hatched as normal larvae. NONA was restricted to th e cytoplasm until the end of cycle 14. We document an active uptake of the NONA-antibody complex into early interphase nuclei from nuclear c ycle 14 onwards, following each mitosis. Significant differences in th e distribution of the protein between fixed and living embryos were ap parent, particularly at high resolution. The NONA protein was localize d in the nuclei of living embryos at discrete sites, most of which lay at the periphery and some of which were tightly clustered. The conste llation of sites changed with time; in some nuclei these changes were fast whereas in other nuclei the pattern was quite stable. These data suggest that specific protein complexes associated with active interph ase chromatin, and possibly chromatin in general, are mobile in the li ving organism.