The σ⁷⁰ family of sigma factors is divided into three groups based on sequence conservation and function. Group 1 includes primary sigma factors essential for cell survival and RNA synthesis. Group 2 consists of sigma factors similar to primary sigmas but not essential for growth. Group 3 includes alternative sigma factors responsible for specific regulons. The σ⁷⁰ family has four conserved regions, with regions 2 and 4 being the most conserved. Region 2 is involved in core binding and promoter recognition, while region 4 is involved in -35 promoter recognition. The σ⁷⁰ family proteins show structural and functional diversity, with some alternative sigmas forming functional subgroups despite low sequence similarity. The conserved regions suggest structural and functional importance. The study provides an updated alignment of σ⁷⁰ family proteins and discusses their evolutionary relationships. The results indicate that sequence divergence among primary sigmas is due to genetic drift, while alternative sigmas show functional constraints. The study also highlights the structural and functional relationships between σ⁷⁰ family proteins and other sigma factors, suggesting that some alternative sigmas may have diverged from a common ancestor. The findings suggest that σ⁷⁰ family proteins are important for transcription initiation and that their evolutionary relationships are complex. The study concludes that σ⁷⁰ family proteins are divided into three groups based on sequence conservation and function, with primary sigmas being the most conserved and alternative sigmas showing functional diversity. The study also notes that bacteriophage sigmas are weakly related to the σ⁷⁰ family.The σ⁷⁰ family of sigma factors is divided into three groups based on sequence conservation and function. Group 1 includes primary sigma factors essential for cell survival and RNA synthesis. Group 2 consists of sigma factors similar to primary sigmas but not essential for growth. Group 3 includes alternative sigma factors responsible for specific regulons. The σ⁷⁰ family has four conserved regions, with regions 2 and 4 being the most conserved. Region 2 is involved in core binding and promoter recognition, while region 4 is involved in -35 promoter recognition. The σ⁷⁰ family proteins show structural and functional diversity, with some alternative sigmas forming functional subgroups despite low sequence similarity. The conserved regions suggest structural and functional importance. The study provides an updated alignment of σ⁷⁰ family proteins and discusses their evolutionary relationships. The results indicate that sequence divergence among primary sigmas is due to genetic drift, while alternative sigmas show functional constraints. The study also highlights the structural and functional relationships between σ⁷⁰ family proteins and other sigma factors, suggesting that some alternative sigmas may have diverged from a common ancestor. The findings suggest that σ⁷⁰ family proteins are important for transcription initiation and that their evolutionary relationships are complex. The study concludes that σ⁷⁰ family proteins are divided into three groups based on sequence conservation and function, with primary sigmas being the most conserved and alternative sigmas showing functional diversity. The study also notes that bacteriophage sigmas are weakly related to the σ⁷⁰ family.