Oligonucleotides in heterogeneous nuclear RNA: similarity of inverted repeats and RNA from repetitious DNA sites

Abstract

A comparison was made by oligonucleotide analysis of 3 fractions of HeLa cell hn[heterogenous nuclear]RNA: the snap-back fraction (ds[double stranded]-hnRNA, 5% of the total), the fraction that self-anneals during prolonged incubation (25% of the total) and the fraction that hybridizes most rapidly to an excess of HeLa cell DNA (rep-hnRNA, 10% of the total). T1 fingerprints of each of these hnRNA fractions were similar to one another and featured the largest T1 fingerprints of each of these hnRNA fractions were similar to one another and featured the largest T1 oligonucleotides of known sequence previously isolated from ds-hnRNA. When hybridized to DNA either in solution or immobolized on filters, the isolated ds-hnRNA and the rep-hnRNA fractions showed similar hybridication kinetics in the Cot [renaturation time] range of intermediate repetitive DNA sequences; the ds-hnRNA and the rep-hnRNA also self-annealed to equal extents in the absence of any DNA. DNA of all buoyant density classes contained the T1 oligonucleotides diagnostic of the ds-hnRNA and the rep-hnRNA. While hnRNA is rich in inverted repeated sequences, cytoplasmic mRNA contains far fewer such sequences.