Transcription in sea urchin. The role of non-histone chromosomal proteins in preventing unproductive binding of RNA polymerase to template

Abstract

In an attempt to understand the regulatory action of the chromosomal structure in transcription, we used Escherichia coli RNA polymerase to study the effect of non-histone chromosomal proteins of gastrula stage embryos of Paracentrotus lividus on two in vitro transcription steps of P. lividus DNA: (1) binding of the enzyme to DNA and (2) initiation of RNA synthesis. In vitro non-histone chromosomal proteins strongly inhibit the low-stability binding of RNA polymerase with DNA, whereas the stable binding of the enzyme with DNA, even at high non-histone chromosomal proteins/DNA ratios, is not affected. As a result of such a selective effect, binary RNA polymerase-DNA complexes characterised by a high stability are preferentially formed in the presence of non-histone chromosomal proteins. We compared the effect exerted by non-histone chromosomal proteins on the binding of RNA polymerase with the effect exerted on the production of RNA chains and found a strong inhibition of the formation of unstable RNA polymerase DNA complexes, while a corresponding inhibition of RNA synthesis was not observed. In particular, under limiting enzyme conditions the relative efficiency of transcriptional versus binding activity is greatly increased by non-histone chromosomal proteins. We discuss the results obtained in the light of the following hypothesis: the high number of trials necessary to localise the relevant DNA sites (promoters) along the eukaryotic chromosomes might be substantially decreased in vivo by a selective alteration of the DNA availability produced by non-histone proteins.