Interspersion and transcription of repeated sequences of rat DNA

Abstract

Repetitive rat DNA reassociated to C o t = 0.1 and deprived of “foldback” sequences showed close interpersion with unique sequences. As measured by electron microscopy, the average length of repetitive segments was about 600 ± 400, and of unique segments 1800–3600 base pairs. Pyrimidine tracts over 80 nucleotides in length were found mainly in foldback and repetitive fractions. Oligo(dT) tracts, 20–30 bases in length prevailed in the DNA fraction reassociated to C o t = 0.1. Repetitive and unique DNA fractions were annealed to Millipore filters and hybridized with hnRNA. Up to 1.6% of repetitive DNA reassociated to C o t = 0.05 showed base complementarity with hnRNA, whereas the comparative figures for DNA reassociated to C o t = 10 and for the unique fraction were 0.8% and 0.3%, respectively. When hybridization of hnRNA was carried out in solution in vast DNA excess, no hybrid formation with repetitive sequences reassociated to C o t = 0.1 was observed, although hybridization with DNA reassociated to C o t = 10 was noticeable.