TEMPLATE STRAND GAP BYPASS IS A GENERAL PROPERTY OF PROKARYOTIC RNA-POLYMERASES - IMPLICATIONS FOR ELONGATION MECHANISMS

It has previously been shown that T7 RNA polymerase is capable of bypa ssing gaps on the template strand ranging in size from 1 to 24 nucleot ides. This as well as other observations suggested a role for the nont emplate strand during elongation. To establish the generality of this gap bypassing event, we have extended these studies to SP6 and Escheri chia coli RNA polymerases. SP6 RNA polymerase bypasses template gaps f rom 1 to 19 nucleotides in size with various degrees of efficiency and produces runoff transcripts of decreasing length corresponding to inc reasing gap size. RNA sequence analysis of the resulting runoff transc ripts revealed that SP6 RNA polymerase faithfully transcribed both par ts of the template strand flanking the gapped region. Similar experime nts were carried out with E. coli RNA polymerase (a multiple subunit e nzyme) and indicate that it is also capable of gap bypass albeit with reduced efficiency compared to T7 and SP6 RNA polymerases. It appears that the ability to bypass gaps present on the DNA template strand is a general property of prokaryotic RNA polymerases. These results have implications with respect to the mechanism of elongation and the role of the nontemplate strand in transcription.