Quantitative Immunochemical Search for Single Stranded DNA in Chromatin

Abstract

SEVERAL observations concerning the structure of DNA in chromatin could be explained if a significant fraction of the nucleic acid existed in the single stranded form in the nucleoprotein. complex. Thus, the altered hypochromicity¹ and circular dichroism spectrum² might arise from a nearly equal mixture of single and double stranded DNA. Furthermore, the finding that DNA in chromatin can be cross-linked to proteins by formaldehyde³, while double stranded DNA is not affected, could be attributed to the presence of single stranded nucleic acid in the complex. Razavi has demonstrated single stranded DNA in cultured lymphocyte chromatin by immunofluorescence⁴, but could not quantify the amount present. Crick⁵ postulated that the control regions of the eukaryotic chromosome might exist as single stranded DNA, and has cited characteristics of the active sites of enzymes and the type of interactions likely to occur in protein-DNA recognition. We tried to measure quantitatively the single stranded DNA in native chromatin by its immune reactivity.