Sequence complexity of poly(A) RNA fromPhysarum polycephalum

Abstract

Poly(A) RNA from S phase, G phase and starved macroplasmodia of Physarum contain mRNA sequences which when translated in vitro, yield similar patterns of polypeptides after fluorography.Reassociation of nick-translated DNA (Cot) allows the isolation of highly labeled single copy DNA which, after saturation hybridization with poly(A) RNA, gives values of 23% for growth and 17% for starvation.Homologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that 22-28% of the genome is transcribed during growth and 12% during starvation and that about half of the cDNA reacts with 0.1% of the genome and could represent 50-80 RNA species, each present in about 1,000 copies per nucleus. Up to 25,000 different RNA species, 1-5 copies each per nucleus, are estimated to be present during growth, and about 15,000 during starvation. Heterologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that the RNA sequences in S and G phase of the cell cycle are similar, with RNA sequences being more abundant in G phase.During starvation about 25% of the sequences present during growth cannot be detected and those sequences present during growth have become diluted during starvation.