Effect ofActinomycin D on theTransfer of Ribonucleic AcidfromNucleus toCytoplasm inLactobacillus acidophilus

After starvation fordeoxyribosides, thedeoxyribonucleic acid(DNA)ofLactobacillus acidophilus isrestricted toa localized region ofthecell. 3H-uracil isfirst incorporated intosucha restricted region butsubsequently isfoundthroughout thecell. Thisspread occursdespite theabsence ofprotein synthesis anda major reduction intherateofribonucleic acid(RNA)synthesis. However, blocking RNA synthesis withactinomycin D restricts incorporation toa localized region ofthe cell. Itisconcluded that uracil isfirst incorporated into RNA inthebacterial nucleus fromwhichitsubsequently spreads through thecell. Actinomycin D could prevent this spread bypreventing thecompletion ofRNA molecules, whichtherefore donot dissociate fromtheDNA template. TheRNA ofeukaryotic cells issynthesized in thenucleus oratthenuclear membrane andsubsequently transferred tothecyt-oplasm (4). A similar demonstration ofthesynthesis ofnuclear ribonucleic acid(RNA)inbacteria isdifficult, since theseparation between nucleus andcytoplasmisdifficult toachieve physically orto visualize. Early attempts todosowerebased on physical fractionation ofRNA fromspheroplasts (5)oronautoradiography intheelectron microscope (6). Themostsignificant ofthese studies wasthatofCaroandForro(2), who studied thedistribution ofpulse-labeled RNA in thinsections ofE.coli. Immediately after the incorporation ofashort pulse of3H-uridine, the majority ofradioactivity waslocated inthose sections containing nuclear regions. However, after a"chase" ofcold uridine, label also could be observed insections without nuclear regions. Inthepresent paper, wedescribe amicrobial system which appears tobewell suited forstudiesoftherelationship between nuclear andcytoplasmic RNA.Thesystem utilizes thelocalization ofdeoxyribonucleic acid(DNA)within Lactobacillus acidophilus after deoxyriboside starvation. We demonstrate thesynthesis ofanuclear RNA whichissubsequently transferred tothe cytoplasm. Thistransfer isinhibited byactinomycin D.