orfatrAb - Molecular characterization of one transcription activator coding gene of the LysR family in Azospirillum brasilense

Abstract

Nitrogen, which is a component of several biomolecules such as nucleic acids and amino acids, is abundant in the atmosphere where, in its gaseous form (N 2 ), it is unavailable for most organisms. However, there are microorganisms, called diazotrophs that are able to convert the atmospheric nitrogen into an assimilable form to other organisms through a process called biological nitrogen fixation. Bacteria of the genus Azospirillum are diazotrophs, free-living or endophytic that are able to associate with grasses like wheat, rice, sugar cane, etc. One of the most used tools for the identification of genes involved in the nitrogen fixation in Azospirillum was the site-direct mutagenesis using the Tn5 transposon. This methodology allowed the isolation of one A. brasilense transconjugant with a capacity of biological nitrogen fixation in vitro that was higher than that of the wild type strain. In the place of transposon insertion into the DNA of this mutant two open reading frames were identified, orfatrAb and orf281, which was interrupted by Tn5. The aim of this work was to determinate the orfatrAb complete nucleotide sequence and the corresponding amino acid sequence which showed great similarity, especially in the amino-terminus, with proteins of the LysR family of transcriptional activators. ORFAtrAb has 297 residues, molecular weight of 33,581.6 kD, isoeletric point of 7.26 and instability index of 33.29. Sequence consensus elements of gene activator proteins involved in the metabolism and in the biological nitrogen fixation were identified in the orfatrAb promoter region.