Skip to Content

Nicole Baldwin

Advisor: Alicia Dombroski, Ph.D.

Obtained Masters degree in Computer Science at University of Tennessee-Knoxville after receiving PhD
Now employed as Bioinformatics Core Manager and Assistant Investigator at Baylor Health Care Center, Dallas, TX

The sigma subunit of eubacterial RNA polymerase is required for recognition of and transcription initiation from, promoter DNA sequences. One family of sigma factors includes those related to the primary sigma factor from E. coli, sigma70. Members of the sigma70 family have four highly conserved domains, of which regions 2 through 4 are present in all members. Region 1 can be subdivided into regions 1.1 and 1.2. Region 1.1 affects DNA binding by sigma70 alone, as well as transcription initiation by holoenzyme. Region 1.2, present and highly conserved in most sigma factors, has not yet been assigned a putative function, although previous work demonstrated that it is not required for either association with the core subunits of RNA polymerase or promoter-specific binding by holoenzyme. This study primarily investigates the functional role of region 1.2 during transcription initiation. In vivo and in vitro characterization of thirty-two single amino acid substitutions targeted to region 1.2 of E. coli sigma70, as well as a deletion of region 1.2, revealed that mutations in region 1.2 can affect promoter binding, open complex formation, initiated complex formation, and the transition from abortive transcription to elongation. The relative degree of solvent exposure of several positions in region 1.2 has been determined, with positions 116 and 122 likely to be located near the surface of sigma70.

During the course of this study, the existence of two “wild type” variants of E. coli sigma70 was discovered. The identity of amino acid 149 has been reported variably as either arginine or aspartic acid in published articles and in online databases. In vivo and in vitro characterization of the two reported variations of E. coli sigma70 (N149 and D149) has determined that the two variants are functionally equivalent. However, in vivo and in vitro characterization of single amino acid substitutions and a region 1.2 deletion in the context of each variant background revealed that the behavior of some mutations are greatly affected by the identity of amino acid 149.

Search pubmed for papers by N Baldwin and AJ Dombroski

Research Info

An Analysis of the Function of Region 1.2 of the Primary Sigma Factor, Sigma70, from Escherichia coli