The Intracellular Transfer of Genetic Information

HISTONE PROTEIN TRANSITION IN DROSOPHILA MELANOGASTER. II. CHANGES DURING EARLY EMBRYONIC DEVELOPMENT

Employing cytochemical methods it was found that during the early embryonic development of Drosophila melanogaster the nuclei contain in sequence two kinds of chromosomal proteins. The cleavage nuclei (as also the pronuclei), until shortly before the blastoderm stage, contain an atypical (or juvenile) histone, stainable with bromophenol blue but not with alkaline fast green. The typical fast green-positive histone appears at the close of the period of the synchronized cleavage mitoses, just before blastulation, when nucleoli are first produced. The amount of DNA of the cleavage nuclei, as determined cytophotometrically, is nearly constant; therefore, the DNA moiety of the nucleohistone complex seems to remain unaffected by the protein shift during embryonic development. The implications of the protein shift in relation to the histone control of gene expression are discussed.

The effect of actidione on mitosis in the slime mold Physarum polycephalum

Actidione, reportedly a specific inhibitor of protein synthesis, was found to reduce the incorporation of labeled amino acids into proteins of the slime mold Physarum polycephalum without drastically inhibiting the incorporation of nucleic acid precursors into RNA. This inhibitor was found to completely block the ensuing mitosis if it was added at any time between telophase and late prophase. Plasmodia given Actidione in late prophase (about the time of nucleolar dissolution) went on through telophase to reconstruction even though nuclear amino acid incorporation was drastically reduced during that period.

EVIDENCE FOR THE EXISTENCE OF FOUR TYPES OF RIBONUCLEOPROTEIN IN THE NERVE CELLS OF THE CEREBELLUM IN THE ADULT CAT

In Helly-fixed cerebella, the toluidine blue – molybdate staining procedure reveals the existence of four distinct types of ribonucleoprotein in both the Purkinje cells of the vermian zone and the multipolar ganglion cells of the fastigial nucleus. These four types of ribonucleoprotein are found in, respectively, the ground substance (nucleolar matrix) of the nucleolus, the intranucleolar vacuoles (nucleolini), the intranuclear paranucleolar masses, and the cytoplasmic Nissl bodies. The relevant observational evidence suggests that the two organelles of the nucleolar apparatus, that is, the nucleolus and paranucleolar masses together with their associated chromocenters, are concerned with distinct synthetic activities with regard to the elaboration of neuronal ribonucleic acids or ribonucleoproteins. The significance of the above findings is discussed in the light of current concepts pertaining to cellular ribonucleoprotein metabolism.

EVIDENCE FOR THE EXISTENCE OF TWO TYPES OF NUCLEOLAR RIBONUCLEOPROTEIN IN ROOT MERISTEMATIC CELLS OF VICIA FABA

In Helly-fixed root meristematic cells of Viciafaba, the toluidine blue – molybdate staining procedure reveals the existence within the interphase nucleus of two metachromatically distinct types of nucleolar ribonucleoprotein. The ribonucleoprotein of the first type stains bluish-green and is associated with the nucleolar matrix. The ribonucleoprotein of the second type takes on a bright purple color and is present inside the nucleolar vacuoles. Evidence is presented suggesting that, during interphase, the nucleolus is the site of active synthesis and of accumulation inside its vacuoles of the second type of ribonucleoprotein.