The hybridisation of [(3)H]poly(uridylic) acid to DNA from Phaseolus aureus Roxb

Ribonucleic acid from the higher plant Matthiola incana. Molecular weight measurements and DNA-RNA hybridisation studies

The percentage of DNA from the crucifer Matthiola incana coding for different types of RNA was measured by filter saturation hybridisation experiments using RNA labelled in vivo. In addition, the melting curves of the various DNA - RNA hybrids formed and the buoyant densities of the DNA sequences complementary to different types of RNA were measured. 1. The RNA preparations used were 25, 18, and 5 S rRNA and 4 S RNA, purified by gel electrophoresis, and poly(A)-containing RNA purified by oligo-(dT)-cellulose chromatography. The molecular weights of the 25 S and 18 S rRNAs, calculated from the mobility in formamide-acrylamide gels relative to Escherichia coli RNA, are 1.25 - 10(6) and 0.64 - 10(6). The rRNA precursor has a molecular weight of approx. 2.1 - 10(6) and the average molecular weight of the poly(A)-containing RNA from both cotyledons and roots is 4 - 10(5). 2. The percentage of the genome, calculated on the basis of double-stranded DNA, coding for these RNAs and the estimated number of genes per haploid DNA amount are approximately 0.46% and 1100 for 25 S plus 18 S rRNA, 0.032% and 3600 for 5 S rRNA and 0.072% and 13 000 for 4 S RNA. In filter hybridisation experiments very little hybridisation of poly(A)-containing RNA was found. A rapidly-hybridising component is attributed to small amounts of contaminating rRNA. 3. M. incana DNA has a main band at 1.697 g - ml-1 in CsCl and a satellite constituting approximately 3% of the DNA, at 1.708 g - ml-1 - 25 and 18 S rRNA hybridise to DNA with a buoyant density of 1.701--2 g - ml-1. The buoyant density of 5 S DNA is slightly less at 1.700--1 g - ml-1. 4. S RNA hybridises to at least two separate regions, one within the main-band DNA and a second lighter component. None of the RNAs tested hybridised to the satellite DNA. The Tm of the DNA - RNA hybrids in 1 X SSC is 89 degrees C for 25 S rRNA, 85 degrees C for 5 S rRNA and 82 degrees C for 4 S RNA. 4. 5 and 4 S RNA preparations contain fragments which hybridise to sequences complementary to high-molecular-weight rRNA. This spurious hybridisation can be eliminated by competition with unlabelled high-molecular-weight RNA.

The measurement of plant polyadenylic acid by hybridisation with radioactive polyuridylic acid

Saturation hybridisation of polyadenylic acid with [(3)H]polyuridylic acid is described. Under conditions of [(3)H]poly(U) excess, poly(A) is detected in the RNA of a number of higher plants. The ribonuclease resistant hybrids melt sharply when subjected to thermal denaturation. Plant RNA which contains poly(A) sequences detected by [(3)H]poly(U) hybridisation is polydisperse in molecular weight. Data presented shows that the amount of poly(A) in plant RNA is variable. This technique is useful for the qualitative and quantitative detection of poly(A) sequences in higher plant RNA.