Chlamydial gene encoding a 70-kilodalton antigen in Escherichia coli: analysis of expression signals and identification of the gene product.

In an attempt to identify chlamydial genes whose native promoters allow them to be expressed in Escherichia coli, we isolated and characterized a chlamydial gene identified by screening a library of chlamydial DNA with antichlamydial antibodies. This gene encodes a 70-kilodalton immunoreactive polypeptide in E. coli hosts. Sequence analysis of the 5' portion of the gene identified its product as the chlamydial homolog of the E. coli ribosomal protein S1. The site of transcription initiation of the mRNA in chlamydiae was determined, and its putative promoter regions were identified. These regions apparently do not function efficiently in E. coli; in vitro transcripts generated by using E. coli RNA polymerase did not start at the authentic chlamydial initiation site. Several in vitro transcripts both larger and smaller than the authentic transcript were seen; presumably, these transcripts result from adventitious promoterlike elements in adjacent chlamydial DNA and may be responsible for the expression of the gene in E. coli.