Site-specific location of covalent DNA-polypeptide complexes in the chicken genome.

A nitrocellulose filter binding assay was applied to isolate and to analyze the fraction of chicken DNA fragments associated with residual nuclear polypeptides resistant to SDS/proteinase K treatment and phenol extraction. It is shown that the DNA-polypeptide complexes retained on nitrocellulose filters are located on a non-random sub-set of DNA sequences. (a) Southern analysis reveals that the fractions of DNA fragments from chicken erythrocytes and from hen oviduct cells associated with the resistant polypeptides have a lower sequence complexity than unfractionated DNA. Moreover, the retained DNA fractions from different cell types of the same species are highly homologous. (b) All DNA fragments of the transcriptionally active and inactive ovalbumin gene map in the DNA fraction passing the filters indicating that the tight DNA-polypeptide complexes are not remnants of transcription complexes. (c) By use of a genomic sub-set library prepared from DNA retained on filters, clones were isolated with sequences mapping specifically in the DNA fraction associated with the tight DNA-polypeptide complexes. The results are consistent with fixed covalent DNA-polypeptide complexes in the chicken genome whose location is essentially identical in different cell types of the same species and apparently determined by DNA signal-sequences.