A method is described that enables a chromatin fraction containing ribosomal DNA (DNA containing sequences coding for rRNA) to be prepared from the macronuclei of growing or stationary cultures of Tetrahymena pyriformis. This material is obtained in yields of between 25 and 75% of the theoretical maximum. The DNA in this fraction was identified as ribosomal DNA on the basis of its density and m...

Aphidicolin, a known inhibitor of eucaryotic deoxyribonucleic acid (DNA) polymerase alpha, efficiently inhibited amplification of ribosomal DNA during oogenesis in Xenopus laevis. DNA polymerase alpha, but not DNA polymerase gamma, as isolated from ovaries, was sensitive to aphidicolin. DNA polymerase beta was not detectable in Xenopus ovary extracts. Therefore, DNA polymerase alpha plays a maj...

Variation of chloroplast DNA and nuclear ribosomal DNA (DNA encoding ribosomal RNA) was studied for five species of white oak native to the eastern United States. Although these species differ in many morphological characters and have different (though overlapping) geographical ranges and ecological tolerances, they are interfertile and often grow in mixed stands, and hybrids are occasionally f...

High-molecular-weight deoxyribonucleic acid (DNA) of Saccharomyces carlsbergensis has been fractionated by sucrose density gradient centrifugation. The main DNA fraction has an average molecular weight of about 500 x 106. A major fraction of the DNA molecules containing sequences homologous to ribosomal ribonucleic acid (RNA) sediments as material of this molecular weight. The remainder sedimen...

INTRODUCTION ................................................................ 262 TECHNICAL ASPECTS OF RNA BIOCHEMISTRYC. .. 263 Size ...263 Compositio.... . 263 Methylation . .263 RNA-DNA Hybridization ...264 Cell Fractionation ......................................................... 264 PATTERNS OF SYNTHESIS OF ANIMAL CELL R.. ........ .. 264 "Rapidly Labeled RNA" and Kinetic Analysis Experi...

Purified ribosomal DNA from Saccharomyces carlsbergensis contains a small proportion of circular DNA molecules with a contour length of 3 micron or integral multiples thereof. Hybridization of yeast ribosomal DNA with 26 S rRNA, using the R-loop technique, reveals that these circular molecules contain sequences complementary to yeast ribosomal RNA. We suggest that these extrachromosomal rRNA ge...