Final answer:
The sigma factor used by E. coli for transcribing house-keeping genes is sigma 70 (σ^70) or RpoD, which binds to specific promoter sequences and directs RNA polymerase to transcribe genes essential for the cell's basic functions.
Step-by-step explanation:
The E. coli uses different sigma factors for transcribing various groups of genes. For house-keeping genes, which are essential for the basic functions of the cell, the primary sigma factor used is the sigma 70 (σ^70) or the RpoD protein. This sigma factor is responsible for the majority of transcription during exponential growth, as it recognizes the promoters of genes that are constantly needed for the survival and normal functioning of the cell.
The σ^70 factor guides the RNA polymerase to the promoters of these house-keeping genes, ensuring that the essential functions of the cell are maintained. Sigma factors are a critical component of bacterial transcription regulation. Without a sigma factor, RNA polymerase can transcribe RNA from random sequences, leading to nonspecific transcription.
However, when a sigma factor is present, it alters this behavior, allowing RNA polymerase to recognize and bind to specific promoter sequences. The σ^70 factor in particular binds to the consensus promoter sequences such as TTGACA and TATAAT, thus initiating the transcription of genes that encode proteins for cell maintenance and regular activity.