Ori-somes, nucleoprotein complexes descending from origin regions of animal chromosomal DNA replication. A micromorphological study

Micromorphology of nucleoprotein (NP) complexes designated according to the ir descent and shape as Ori-somes is presented. These NP complexes of three different types harbor molecules of cytoplasmic "small" polydisperse DNA, which descend from origin regions of chromosomal DNA replication and are eq uipped, as shown previously, with early DNA-synthesizing activities. By neg ative staining the Ori-somes are visualized as particles of irregular shape , sometimes of a subunit-like structure. Micromorphological differences in size and structural compactness noted among individual Ori-somes are depend ent on their type similarly as earlier shown physico-chemically and biochem ically. Such differences were also confirmed by two different spreading tec hniques. The most unravelled structures with electron diffuse centers belon g to Ori-somes of component B associated with most active DNA synthesis. In contrast, the Ori-somes of components A and C, associated with pronounced RNA synthesis, revealed large electron-dense centers. The incidence of repl icative structures present in Ori-somes corresponds with the level of their DNA-synthesizing activities.