Transcription of the isoamylase gene (iam) in Pseudomonas amyloderamosa SB-15

Abstract

S1 nuclease mapping of RNA prepared from Pseudomonas amyloderamosa SB-15 suggested that the iam gene coding for isoamylase (glycogen 6-glucanohydrolase [EC 3.2.1.68]) is transcribed from two promoters. The transcription start site for the upstream promoter (termed P1) was located -182 base pairs from the first nucleotide of the initiation codon of iam, whereas the start site for the downstream promoter (termed P2) was 99 base pairs downstream of the P1 start site. Transcriptions from these promoters were induced by maltose and were not repressed by glucose. The promoter regions contained sequences homologous to the consensus sequence recognized by sigma 54 RNA polymerase of enteric bacteria and found in promoters of other Pseudomonas species. Northern (RNA) hybridization provided evidence that the iam gene is transcribed as monocistronic mRNAs with an approximate size of 2.6 kilobases.