High molecular weight RNA synthesized in nucleoli of higher plants

Preservation of algal and higher plant ribosomal RNA integrity during extraction and electrophoretic quantitation

Isolation of high molecular weight ribosomal RNA from the wall-less alga Olisthodiscus luteus and the angiospermous plant Sauromatum guttatum is described. It has been found that a buffer which contains magnesium must be used to successfully isolate Olisthodiscus rRNA whereas the isolation of intact Sauromatum rRNA requires a buffer system containing a high amount of the chelator EDTA. Sauromatum but not Olisthodiscus extracts were contaminated with ribonuclease unless the inhibitor diethylpyrocarbonate was used during the ribonucleic acid extraction procedure. Nuclease levels were monitored by coincubating [3H]-labeled Escherichia coli ribosomal RNA with the experimental RNA samples. The effects of detergents on the isolation and quantitation of RNA are presented, and methods to avoid loss of highly thermolabile plant ribosomal RNA species are discussed.

Non-coordinated histone synthesis with DNA replication and close temporal association of ribosomal proteins and rRNA syntheses in germinating Vicia faba embryos

Syntheses of DNA, RNA and basic proteins during germination of Vicia faba seeds were examined. Incorporation of [3H]thymidine into DNA reached a maximum peak at approximately 34 h after beginning imbibition and the phase of DNA replication was preceded by active RNA synthesis. When Vicia embryos were labeled with [3H]lysine or E13H]arginine, these isotopes were incorporated into ribosomal proteins and histones. The incorporation studies indicated that the synthesis of ribosomal structural proteins is closely linked with rRNA synthesis and histone synthesis occurs during and also before the phase of DNA replication. Polyacrylamide gel electrophoresis of Vica histones indicated that some histones of Vicia embryos differ from corresponding calf thymus histones in their mobilities.

Ribosomal cistrons in higher plant cells. I. A definitive scheme for the maturation pathway of the primary transcriptional product of ribosomal cistrons in Acer pseudoplatanus L. cells

1. Four precursor ribosomal RNAs have been previously characterized in cultured sycamore cells (Acer pseudoplatanus L.). The present paper reports a study of the two smallest ones. 2. (Me-3H)-labelling of the precursor and mature rRNAs has been submitted to kinetic analysis. From pulse-chase experiments it is concluded that the 27S and 20S precursor rRNAs behave like intermediate molecules in the maturation of the 42S and 36S precursor rRNAs into the 26S and 17S components. They are direct precursors to the cytoplasmic and mature rRNAs. 3. Base-composition analyses have been performed on carefully purified molecules. They show that the 27S and 20S precursor rRNAs arise from a single cleavage of the 36S precursor rRNA. In addition, they strongly suggest that the 27S and 20S precursor rRNAs can be taken as specific precursors to the 26S and 17S rRNAs, respectively. These results are reinforced by DNA - RNA hybridization experiments, the measured values being in good agreement with the theoretical ones expected from a specific relationship between the four smallest molecules. Base-compositions of the conserved and non-conserved nucleotide sequences of the primary transcriptional product have been estimated or calculated. 4. On the basis of the present results and those previously reported, a scheme for the biosynthesis of ribosomal RNA in sycamore cells is proposed.

Rapidly labeled intermediates in DNA replication in higher plants

In detached Vicia embryos, the incorporation of [3-H] thymidine into DNA starts at about 25 h after the beginning of imbibition and reaches maximum at about 33 h. The DNA synthesized during the first replication phase was extracted. Alkaline sucrose density-gradient analyses of the DNA indicated the occurrence of several short pieces of rapidly labeled DNA having sedimentation values of approx. 10 S and 14 S, after a pulse for 5 to 10 min. Prolonged labeling and chase incubation led to a shift of the shorter fragments to longer ones of 19 S and 22 S or more, thus indicating the nature of intermediates during DNA replication of these short fragments.

Early ribonucleic acid synthesis during the germination of rye (Secale cereale) embryos and the relationship to early protein synthesis

Incorporation studies with radioactive precursors showed that synthesis of protein and RNA is initiated in germinating embryos of rye within the first hour of imbibition of water. By polyacrylamide-gel fractionations of radioactive nucleic acid components, the appearance of products of transcription of the genome was shown to follow the sequence: heterogeneous (ribonuclease-sensitive) RNA, 4S and 5S RNA by 20min, 31S and 25S rRNA by 40min, and 18S RNA by 60min. "Fingerprint' analysis of T1-ribonuclease digests show that all the large oligonucleotides present in 25S and 18S RNA are present in the 31S species, indicating that 31S RNA is the precursor rRNA molecule to both 25S and 18S RNA. The importance of these early RNA syntheses and in particular the possible template function of the heterogeneous RNA is discussed in relation to the concept of long-lived mRNA and the coding for protein synthesis in the first hours of germination.