Book of Abstracts: Albany 2011
June 14-18 2011
©Adenine Press (2010)
Transcription Blockage by Guanine-Rich DNA Sequences and Possible Effects on Transcription of Nascent RNA Binding to DNA
Various DNA sequences that interfere with transcription due to their unusual structural properties have been implicated in the regulation of gene expression and with genomic instability. An important example is sequences containing G-rich homopurine-homopyrimidine stretches, for which unusual transcriptional behavior is implicated in regulation of immunogenesis and in other processes, such as genomic translocations and telomere function. To elucidate the mechanism of the effect of these sequences on transcription we have studied T7 RNA polymerase transcription of G-rich sequences in vitro. We have shown that these sequences produce significant transcription blockage in an orientation-, length- and supercoiling-dependent manner. Based upon the effects of various sequence modifications, solution conditions and substitution of inosine or deazaguanosine for guanosine, we conclude that transcription blockage is due to formation of unusually stable RNA/DNA hybrids, which could be further exacerbated by triplex formation. These structures are likely responsible for transcription-dependent replication blockage by G-rich sequences in vivo (1). We have also analyzed the general effect of stable nascent RNA binding to DNA theoretically, and we conclude that such anchoring could interfere with transcription downstream from the anchoring point (2).
Supported by a grant CA77712 from the National Cancer Institute, NIH
Boris P. Belotserkovskii1*
1Department of Biology, Stanford University, Stanford, CA 94305