Ribosomal RNA synthesis in the mycelium of Phycomyces blakesleeanus. High molecular weight RNA.

Total RNA was extracted from 24 h old mycelia of Phycomyces blakesleeanus which had been grown in liquid culture. Heavy molecular weight RNA was fractionated on 2.6% polyacrylamide gels. 1. The main cytoplasmic ribosomal RNA fractions had molecular weights of 1.34 and 0.72-16(6). 2. [3H]Uridine pulse labelling of cultures revealed an initial ribosomal RNA precursor of molecular weight 2.5-10(6). 3. An intermediate precursor for the 1.34 - 10(6) dalton peak was found, having a molecular weight of 1.6-10(6). 4. Pulse-chase experiments, using [3H]methionine, showed the flow of synthesis as being (see article). 5. Mature 0.72-10(6) dalton RNA appeared prior to the 1.34-10(6) dalton RNA but no immediate precursor for it was detected.