ROLE OF SULFUR IN THE CELL DIVISION OF CHLORELLA, WITH SPECIAL REFERENCE TO THE SULFUR COMPOUNDS APPEARING DURING THE PROCESS OF CELL DIVISION. I.

1. The role of sulfur in the cell division of Chlorella was studiedby following the fate of the sulfur supplied to the sulfur-deficientcells using ³⁵S as a tracer.
2. The sulfur-deficient cells whichwere unable to perform celldivision were made capable of divisionby the provision of ³⁶S-labeledsulfate under non-photosynthesizingconditions. Soon after theprovision of sulfate the labeledsulfur went rapidly into thecold perchloric acid (PCA)-solublefraction of algal cells,almost entirely in the form of sulfateand/or some other inorganicsulfur substance (s). With the lapseof time, more or less remarkablechanges occurred in the patternof ³⁵S-distribution in differentfractions of cell material.It was noticed that, at the onsetof cell division, a sulfur-containingpeptide-nucleotide compound(s)(SPN), which has been reportedearlier, appeared in a largequantity in the cold PCA-solublefraction, and that its quantitydecreased gradually during thesubsequent process of cell division,suggesting that the compoundwas transformed into some othersubstance (s), presumably withits nucleotide moiety going intonucleic acids and the peptidemoiety going into some essentialproteins.
3. Another noteworthyphenomenon observed during the process ofcell division wasthe incorporation of ³⁶S in a group of hotPCA-soluble substances.These sulfur substances were revealedto be sulfur-containingnucleotidic compounds, which might possiblybe some essentialcomponents of, or substances in close relationto, deoxypentosenucleic acid (DNA).

(Received March 1, 1960; )