Condiciones ambientales que afectan la expresión del gen suoM: un factor sigma de estrés en M. smegmatis

Sigma factors associate with the RNA polymerases and confer specificity in the recognition of promoter regions. This provides a transcriptional regulatory level, that determines that a set of genes is expressed according to the physiological necessities of bacterial cell. The sequence analysis of the region of replication origin of Mycobacterium smegmatis revealed the presence of a reading frame with capacity to codify a sigma factor of the ECF subfamily (“extracytoplasmic function”), which are characterized by directing the transcription of genes in response to changes in the environmental conditions. Transcriptional fusions PsuoM-lacZ’ in operon fusion plasmid pJEM15 were constructed with the objective of identifying the environmental conditions that stimulate the expression of the isolated gene, named suoM (“sigma linked to the origin in mycobacteria”), The constructions were introduced by electroporation in M. smegmatis and the cells were grown under different environmental stress conditions. The promoter activity of the gene suoM was measured by B-galactosidasa expression. An increase of 2.0-3.5 times in the promoter activity was observed when the cells were transferred to 45°C and when the culture reached stationary growth phase. The results suggest that suoM could be involved in the regulation of gene expression in conditions of high temperature and in the stationary growth phase, inductive conditions that could have some significance in the pathogenic potential of mycobacteria and the ability of M. tuberculosis to cause latent infection. Resumen: Los factores sigma se asocian a la ARN polimerasa y le confieren especificidad de reconocimiento de regiones promotoras. Esto provee un nivel de regulación transcripcional, que determina que un grupo de genes sea expresado de acuerdo a las necesidades fisiológicas de la célula bacteriana. El análisis de secuencia de la región del origen de replicación de Mycobacterium smegmatis reveló la presencia de un marco de lectura con capacidad codificante para un factor sigma de la subfamilia ECF (“extracytoplasmic function”), los cuales se caracterizan por dirigir la transcripción de genes en respuesta a cambios en las condiciones ambientales. Con el objetivo de identificar las condiciones ambientales que estimulan la expresión del gen aislado, designado suoM (“sigma unido al origen en micobacterias”), se construyeron fusiones transcripcionales PsuoM-lacZ’ sobre el plásmido de fusión de operones pJEM15. Las constru