Elucidation of the relationships between LexA-regulated genes in the SOS response.

Monitoring the expression of many genes under different conditions is a common approach for investigating gene relationships. In particular, the monitoring sheds light on the biological phenomena in which many genes are coordinately expressed. In this study, we analyzed the expression profiles of LexA-regulated genes after UV irradiation, to elucidate the genes related to the SOS response, which involves coordinately regulated gene expression. By the two-gene relationship analysis, the LexA-regulated genes were highly correlated with the genes involved in the DNA repair functions. The LexA-regulated genes with highly significant probability were divided into two groups: the LexA-regulated genes that were mutually related within them were related to the genes with DNA repair functions, while the LexA-regulated genes that were less related within them showed lower relation to the genes with DNA repair functions. By a multiple gene relationship analysis, the two types of LexA-regulated genes were clearly clustered, and the inferred network between the clusters indicated their sequential relationship of clusters in the two groups of LexA-regulated genes in the SOS response; the former type of genes emerged in the early stage of the SOS response upon the signal transduction by membrane proteins, cessation of cell division and recognition of DNA damage, and the latter type emerged in a later stage, and functioned in the repair mechanism and the resumption of DNA replication.