RecA intron and ribose mutarotase

Abstract

The self-splicing introns are rarely found in bacteria and bacteriophages and they are classified into group I and II according to their structural features and splicing mechanisms. While the group I introns are occasionally found in protein coding regions of phage genomes and in several tRNA genes of bacteria, they were never found so far in protein-coding regions of bacterial genomes. The presence of intron in the recA gene of Bacillus anthracis was found for the first time. It was initially found by DNA sequencing as an intervening sequence (IVS) in the putative recA gene. Previously, the IVS was demonstrated to be an intron by RT-PCR and predicted secondary structure. The in vitro splicing with labeled free GTP confirmed the fact that it is a group I intron. The RecA protein of B. anthracis expressed in E. coli was functional in its ability to complement a recA defect. When recA-negative E. coli cells were irradiated with UV, the Bacillus RecA reduced the UV susceptibility of the recA mutant, regardless of the presence of intron. The difference due to the presence of intron was only found in growth. Based on the fact that the related mycobacterial species contain inteins in the RecA protein at the corresponding site of the Bacillus intron, the presence of an intron in the B. anthracis recA gene appears to provide an important clue to the origin of inteins. D-ribose uptake occurs through the ABC transporter system encoded by rbsDACBKR operon. Except rbsD, other proteins`` function is mostly known. When rbsD and rbsACBK were overexpressed, the cells showed lethality. The suppressors relieving lethality had changes in specific residues that form a secondary structure in mRNA. When mutations breaking the RNA secondary structure was introduced, the lethality was not abolished. Another mutant producing mRNA without being translated did not show the lethality phenotype. Actually, the mutant hardly expresses the transcript of rbsD. This also confirms that the trans...