Studies on Plastid-Nuclei (Nucleoids) inNicotiana tabacumL. IV. Association of Chloroplast-DNA with Proteins at Several Specific Sites in Isolated Chloroplast-Nuclei

摘要

When chloroplast-nuclei (cp-nuclei), isolated from tobacco mesophyll protoplasts, were directly digested by restriction enzymes and analyzed by agarose gel electrophoresis, the migration of several restriction fragments was greatly inhibited during the electrophoresis. When the digested cp-nuclei were treated with SDS and proteinase K prior to electrophoresis, all the restriction fragments migrated normally and the electrophoretic pattern was the same as that generated by similarly restricted, purified chloroplast-DNA (cp-DNA). Use of a newly developed method,“reciprocal electrophoresis”, proved that these fragments were bound so tightly to certain DNA-binding protein(s) that the fragments were trapped in the gel slot. These fragments corresponded to at least four sites of the cp-DNA. By contrast, when proplastid-nuclei (pp-nuclei) isolated from tobacco cultured cells were analyzed in the same way, no restriction fragments were trapped in the gel slot.These results, taken together, suggest that a DNA-binding protein(s) is present in cp-nuclei, but not in pp-nuclei, and binds tightly to the four sites of the cp-DNA. Therefore, the molecular architecture of cp-nuclei is clearly different from that of pp-nuclei. The DNA-binding protein(s) may have some function(s) specific to cp-nuc