Relationship between single-stranded DNA isolated from cultured muscular cells during differentiation and the transcription of messenger RNA.

Single-stranded DNA (ssDNA), equivalent to about 2% of the total nuclear DNA, was isolated by an improved method of hydroxyapatite chromatography from native nuclear DNA of rat myoblast cells and myotubes of the L6 line. Small quantities of 125I-labelled ssDNA were annealed with a large excess of unlabelled DNA, cytoplasmic RNA and mRNA from myoblasts or myotubes. The results indicated that ssDNA belongs to the non-repetitious portion of the cell genome and is formed of two distinct molecular fractions. The major ssDNA fractions (75%) consist of non-self-reassociating DNA sequences and the minor fraction (25%) consists of self-reassociating DNA sequences. About 30--32% and 25--26% of ssDNA from myoblast represent DNA sequences complementary to total cytplasmic RNAs and polyadenylated RNAs respectively. Hybridizations of ssDNA with an excess of RNA from myoblasts and/or myotubes show differences in the abundance and the diversity of mRNA during mascular differentiation. These differences were confirmed by DNA-driven reactions between 125I-labelled polyadenylated RNA and ssDNA in great excess.