Heterogeneous Labelling of Acid-soluble Nucleoside 5′-Monophosphates during Short in vivo Incubation with Phosphate-³²P

Abstract

A PROBABLE explanation of the heterogeneous ³²P-labelling of 5′-nucleotide units of ribonucleic acid of rat liver¹ and deoxyribonucleic acid of thymine-requiring E. coli ² after brief incubation with phosphate-³²P is that the carbon-bound phosphate groups of postulated precursor 5′-nucleotides³ become labelled at unequal rates. Brumm, Potter and Siekevitz⁴ have studied the incorporation of phosphorus-32 into acid-soluble nucleotides of rat liver, but the isolated guanylic and uridylic acids were noted to contain impurities. Because there is little direct in vivo evidence that 5′-nucleotides actually are the building blocks in biosynthesis of nucleic acids in mammalian tissues, we have re-investigated the status of labelling after a short time of incubation, when unequal synthetic rates should be most easily observable.