THE GLUTAMIC-ACID RESIDUE AT AMINO-ACID-261 OF THE ALPHA-SUBUNIT IS ADETERMINANT OF THE INTRINSIC EFFICIENCY OF RNA-POLYMERASE AT THE METECORE PROMOTER IN ESCHERICHIA-COLI

A mutation in the rpoA gene (which encodes the alpha subunit of RNA po lymerase) that changed the glutamic acid codon at position 261 to a ly sine codon decreased the level of expression of a metE-lacZ fusion 10- fold; this decrease was independent of the MetR-mediated activation of metE-lacZ. Glutamine and alanine substitutions at this position are a lso metE-lacZ down mutations, suggesting that the glutamic acid residu e at position 261 is essential for metE expression. In vitro transcrip tion assays with RNA polymerase carrying the lysine residue at codon 2 61 indicated that the decreased level of metE-lacZ expression was not due to a failure of the mutant polymerase to respond to any other trai ls-acting factors, and a deletion analysis using a lambda metE-lacZ ge ne fusion suggested that there is no specific cis-acting sequence upst ream of the -35 region of the metE promoter that interacts with the al pha subunit. Our data indicate that the glutamic acid at position 261 in the ex subunit of RNA polymerase influences the intrinsic ability o f the enzyme to transcribe the metE core promoter.