Analysis of long pyrimidine polynucleotides in HeLa cell nuclear DNA: absence of polydeoxythymidylate.

HeLa cell nuclear DNA contains an unexpectedly large amount of long pyrimidine polynucleotides. These sequences were detected in DNA labeled with [(3)H] thymidine by treatment with formic acid-diphenylamine and subsequent analysis by polyacrylamide gel electrophoresis. About 0.5% of the total thymine residues were found in polynucleotides that migrated more slowly than 4S RNA. No polynucleotides of comparable size were detected in Escherichia coli DNA. The pyrimidine polynucleotides contained no pure poly(dT) sequences (less than 0.0015% of the total residues), as judged by thermal chromatography of a complex formed with poly(A).